diff --git a/cmd/eirctl/run.go b/cmd/eirctl/run.go
index b145d86b..bb295db2 100644
--- a/cmd/eirctl/run.go
+++ b/cmd/eirctl/run.go
@@ -21,6 +21,8 @@ var (
 
 type runFlags struct {
 	showGraphOnly, detailedSummary bool
+	contextName                    string
+	imports                        []string
 }
 
 type runCmd struct {
@@ -52,6 +54,9 @@ func newRunCmd(rootCmd *EirCtlCmd) {
 			if err != nil {
 				return err
 			}
+			if err := runner.applyImports(conf); err != nil {
+				return err
+			}
 			// display selector if nothing is supplied
 			if len(args) == 0 {
 				selected, err := cmdutils.DisplayTaskSelection(rootCmd.ctx, conf, false)
@@ -85,6 +90,9 @@ func newRunCmd(rootCmd *EirCtlCmd) {
 			if err != nil {
 				return err
 			}
+			if err := runner.applyImports(conf); err != nil {
+				return err
+			}
 			taskRunner, argsStringer, err := rootCmd.buildTaskRunner(args, conf)
 			if err != nil {
 				return err
@@ -92,6 +100,9 @@ func newRunCmd(rootCmd *EirCtlCmd) {
 			if argsStringer.pipelineName == nil {
 				return fmt.Errorf("pipeline: %s is %w", args[0], ErrSpecifiedObjectIsNotFound)
 			}
+			if runner.flags.contextName != "" {
+				return errors.New("the context flag can only be used when running a task")
+			}
 			return runner.runPipeline(argsStringer.pipelineName, taskRunner, conf.Summary)
 		},
 	})
@@ -108,6 +119,9 @@ func newRunCmd(rootCmd *EirCtlCmd) {
 			if err != nil {
 				return err
 			}
+			if err := runner.applyImports(conf); err != nil {
+				return err
+			}
 			runner.conf = conf
 			taskRunner, argsStringer, err := rootCmd.buildTaskRunner(args, conf)
 			if err != nil {
@@ -116,7 +130,7 @@ func newRunCmd(rootCmd *EirCtlCmd) {
 			if argsStringer.taskName == nil {
 				return fmt.Errorf("task: %s is %w", args[0], ErrSpecifiedObjectIsNotFound)
 			}
-			return runner.runTask(argsStringer.taskName, taskRunner)
+			return runner.runTask(runner.taskWithContext(argsStringer.taskName), taskRunner)
 		},
 	})
 
@@ -138,6 +152,8 @@ func newRunCmd(rootCmd *EirCtlCmd) {
 
 	rc.PersistentFlags().BoolVarP(&f.showGraphOnly, "graph-only", "", false, "Show only the denormalized graph")
 	rc.PersistentFlags().BoolVarP(&f.detailedSummary, "detailed", "", false, "Show detailed summary, otherwise will be summarised by top level stages only")
+	rc.PersistentFlags().StringVarP(&f.contextName, "context", "", "", "override the context used when running a task")
+	rc.PersistentFlags().StringArrayVarP(&f.imports, "import", "", nil, "import an additional config file, can be repeated; entries in imported files take precedence over any existing ones with the same name")
 
 	rootCmd.Cmd.AddCommand(rc)
 }
@@ -145,11 +161,14 @@ func newRunCmd(rootCmd *EirCtlCmd) {
 func (r *runCmd) runTarget(taskRunner *runner.TaskRunner, conf *config.Config, argsStringer *argsToStringsMapper) (err error) {
 
 	if argsStringer.pipelineName != nil {
+		if r.flags.contextName != "" {
+			return errors.New("the context flag can only be used when running a task")
+		}
 		return r.runPipeline(argsStringer.pipelineName, taskRunner, conf.Summary)
 	}
 
 	if argsStringer.taskName != nil {
-		if err := r.runTask(argsStringer.taskName, taskRunner); err != nil {
+		if err := r.runTask(r.taskWithContext(argsStringer.taskName), taskRunner); err != nil {
 			return fmt.Errorf("task `%s` failed: %w", argsStringer.taskOrPipelineName, err)
 		}
 	}
@@ -157,6 +176,30 @@ func (r *runCmd) runTarget(taskRunner *runner.TaskRunner, conf *config.Config, a
 	return nil
 }
 
+// applyImports merges any files supplied via the repeatable --import flag into
+// conf, with entries in those files taking precedence over any name clashes.
+func (r *runCmd) applyImports(conf *config.Config) error {
+	if len(r.flags.imports) == 0 {
+		return nil
+	}
+	cl := config.NewConfigLoader(conf)
+	if _, err := cl.LoadImports(r.flags.imports); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (r *runCmd) taskWithContext(t *task.Task) *task.Task {
+	if r.flags.contextName == "" {
+		return t
+	}
+
+	taskWithContext := task.NewTask(t.Name)
+	taskWithContext.FromTask(t)
+	taskWithContext.Context = r.flags.contextName
+	return taskWithContext
+}
+
 func (r *runCmd) runPipeline(g *scheduler.ExecutionGraph, taskRunner *runner.TaskRunner, summary bool) error {
 	sd := scheduler.NewScheduler(taskRunner)
 	defer sd.Finish()
diff --git a/cmd/eirctl/run_test.go b/cmd/eirctl/run_test.go
index bfea804d..85fcceb2 100644
--- a/cmd/eirctl/run_test.go
+++ b/cmd/eirctl/run_test.go
@@ -25,9 +25,27 @@ func Test_runCommand(t *testing.T) {
 	t.Run("correct with task specified", func(t *testing.T) {
 		cmdRunTestHelper(t, &cmdRunTestInput{args: []string{"-c", "testdata/graph.yaml", "run", "task", "graph:task1", "--raw"}, exactOutput: "hello, world!\n"})
 	})
+	t.Run("overrides the context for an implicit task", func(t *testing.T) {
+		cmdRunTestHelper(t, &cmdRunTestInput{args: []string{"-c", "testdata/task.yaml", "run", "task:context:override", "--context", "context:env", "--raw"}, exactOutput: "supplied-by-context\n"})
+	})
+	t.Run("overrides the context for an explicit task", func(t *testing.T) {
+		cmdRunTestHelper(t, &cmdRunTestInput{args: []string{"-c", "testdata/task.yaml", "run", "task", "task:context:override", "--context", "context:env", "--raw"}, exactOutput: "supplied-by-context\n"})
+	})
+	t.Run("import flag overrides an existing context on clash", func(t *testing.T) {
+		cmdRunTestHelper(t, &cmdRunTestInput{args: []string{"-c", "testdata/task.yaml", "run", "task", "task:context:override", "--context", "context:env", "--import", "testdata/cli-import-override.yaml", "--raw"}, exactOutput: "supplied-by-cli-import\n"})
+	})
+	t.Run("import flag adds a new task", func(t *testing.T) {
+		cmdRunTestHelper(t, &cmdRunTestInput{args: []string{"-c", "testdata/task.yaml", "run", "task", "task:from:cli:import", "--import", "testdata/cli-import-override.yaml", "--raw"}, exactOutput: "hello from cli import\n"})
+	})
+	t.Run("import flag not supplied does not affect existing behaviour", func(t *testing.T) {
+		cmdRunTestHelper(t, &cmdRunTestInput{args: []string{"-c", "testdata/task.yaml", "run", "task", "task:context:override", "--context", "context:env", "--raw"}, exactOutput: "supplied-by-context\n"})
+	})
 	t.Run("correct with pipeline specified", func(t *testing.T) {
 		cmdRunTestHelper(t, &cmdRunTestInput{args: []string{"-c", "testdata/graph.yaml", "run", "pipeline", "graph:pipeline1", "--raw"}, output: []string{"hello, world!\n"}})
 	})
+	t.Run("rejects a context override for a pipeline", func(t *testing.T) {
+		cmdRunTestHelper(t, &cmdRunTestInput{args: []string{"-c", "testdata/graph.yaml", "run", "pipeline", "graph:pipeline1", "--context", "context:env", "--raw"}, errored: true, output: []string{"context flag can only be used when running a task"}})
+	})
 	t.Run("correct prefixed output", func(t *testing.T) {
 		t.Setenv("EIRCTL_CONFIG_FILE", "testdata/graph.yaml")
 		cmdRunTestHelper(t, &cmdRunTestInput{args: []string{"--output=prefixed", "run", "graph:pipeline1"}, output: []string{"graph:task1", "graph:task2", "graph:task3", "hello, world!"}})
diff --git a/cmd/eirctl/testdata/cli-import-override.yaml b/cmd/eirctl/testdata/cli-import-override.yaml
new file mode 100644
index 00000000..3ca9b324
--- /dev/null
+++ b/cmd/eirctl/testdata/cli-import-override.yaml
@@ -0,0 +1,12 @@
+# yaml-language-server: $schema=../../../schemas/schema_v1.json
+# fixture used to verify entries supplied via `--import` on the CLI
+# take precedence over any existing entries with the same name
+
+contexts:
+  context:env:
+    env:
+      FOO: supplied-by-cli-import
+
+tasks:
+  task:from:cli:import:
+    command: "echo 'hello from cli import'"
diff --git a/cmd/eirctl/testdata/task.yaml b/cmd/eirctl/testdata/task.yaml
index 31a63823..0d59b6c6 100644
--- a/cmd/eirctl/testdata/task.yaml
+++ b/cmd/eirctl/testdata/task.yaml
@@ -1,6 +1,9 @@
 # yaml-language-server: $schema=../../../schemas/schema_v1.json
 
 contexts:
+  context:env:
+    env:
+      FOO: supplied-by-context
   context:v1:
     executable:
       bin: foo
@@ -20,6 +23,8 @@ contexts:
         - HOME
         - PATH
 tasks:
+  task:context:override:
+    command: "echo '{{ .Env.FOO }}'"
   task:task1:
     command: "echo 'This is {{index .ArgsList 0}} argument'"
     env:
diff --git a/docs/import.adoc b/docs/import.adoc
index 638466d9..094a2ea9 100644
--- a/docs/import.adoc
+++ b/docs/import.adoc
@@ -50,3 +50,20 @@ Set `GIT_SSH_PASSPHRASE` when the selected SSH key is encrypted with a passphras
 === Filesystem
 
 Filesystem imports support relative and absolute paths.
+
+=== Command line
+
+`eirctl run` accepts a repeatable `--import` flag to bring in additional config files at execution time, without editing the project's config file:
+
+[source,bash]
+----
+eirctl run task1 --import ./local/context-overrides.yaml
+eirctl run pipeline pipeline1 --import ./local/context-overrides.yaml --import ./local/extra-tasks.yaml
+----
+
+This is useful when working with new or unverified contexts during development, avoiding the risk of accidentally committing them to the tracked config file.
+
+[IMPORTANT]
+====
+Unlike the `import:` directive in a config file, which errors on a name clash, entries supplied via `--import` on the command line take precedence over any existing tasks, pipelines, or contexts with the same name.
+====
diff --git a/docs/index.adoc b/docs/index.adoc
index 8d5123e8..069a3f8c 100644
--- a/docs/index.adoc
+++ b/docs/index.adoc
@@ -13,6 +13,8 @@ include::installation.adoc[]
 
 include::import.adoc[]
 
+include::tasks.adoc[]
+
 include::artifacts.adoc[]
 
 include::watchers.adoc[]
diff --git a/docs/tasks.adoc b/docs/tasks.adoc
new file mode 100644
index 00000000..95016bfb
--- /dev/null
+++ b/docs/tasks.adoc
@@ -0,0 +1,31 @@
+== Running tasks
+
+Tasks can use a context configured in the eirctl configuration file. When testing
+a task in another context, use the `--context` option with `eirctl run`:
+
+[source,bash]
+----
+eirctl run task task1 --context context:v2
+----
+
+The option also works with the short form of the command, where the task name
+is supplied without the `task` subcommand:
+
+[source,bash]
+----
+eirctl run task1 --context context:v2
+----
+
+`--context` overrides the context configured on the selected task for that
+invocation. The value must be the name of a context defined in the loaded
+configuration, including any files supplied with `--import`.
+
+The option applies only to tasks. It cannot be used when running a pipeline:
+
+[source,bash]
+----
+eirctl run pipeline pipeline1 --context context:v2
+----
+
+The command returns an error when a context override is supplied for a
+pipeline.
diff --git a/internal/config/config.go b/internal/config/config.go
index ed0f89c6..36ad7867 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -68,6 +68,25 @@ func (cfg *Config) merge(src *Config) error {
 	return nil
 }
 
+// mergeOverride merges src into cfg, with values in src taking precedence
+// over any existing entries in cfg on a name clash (e.g. contexts, tasks, pipelines).
+//
+// Used when merging config supplied via CLI (e.g. `--import`) on top of the
+// already loaded config.
+func (cfg *Config) mergeOverride(src *Config) error {
+	defer func() {
+		if err := recover(); err != nil {
+			logrus.Error(err)
+		}
+	}()
+
+	if err := mergo.Merge(cfg, src, mergo.WithOverride); err != nil {
+		return err
+	}
+
+	return nil
+}
+
 func buildFromDefinition(def *ConfigDefinition, lc *loaderContext) (cfg *Config, err error) {
 	cfg = NewConfig()
 
diff --git a/internal/config/loader.go b/internal/config/loader.go
index 1b1aeba1..8a1bfb9d 100644
--- a/internal/config/loader.go
+++ b/internal/config/loader.go
@@ -130,6 +130,39 @@ func (cl *Loader) Load(file string) (*Config, error) {
 	return cl.Validate()
 }
 
+// LoadImports loads additional standalone config files, e.g. supplied via the
+// `--import` CLI flag, and merges them into the already loaded config.
+//
+// Unlike the `import:` directive in a config file, entries in these files take
+// precedence over any existing entries with the same name (contexts, tasks,
+// pipelines etc.), allowing CLI supplied imports to override the loaded config.
+func (cl *Loader) LoadImports(files []string) (*Config, error) {
+	for _, file := range files {
+		if !utils.IsURL(file) && !filepath.IsAbs(file) {
+			file = path.Join(cl.dir, file)
+		}
+
+		def, err := cl.load(schema.ImportEntry{Src: file})
+		if err != nil {
+			return nil, err
+		}
+
+		importedCfg, err := buildFromDefinition(def, &loaderContext{Dir: cl.dir})
+		if err != nil {
+			return nil, err
+		}
+
+		if err := cl.dst.mergeOverride(importedCfg); err != nil {
+			return nil, err
+		}
+		logrus.Debugf("import %s loaded", file)
+	}
+
+	cl.dst.Variables.Set("Root", cl.dir)
+
+	return cl.Validate()
+}
+
 // LoadGlobalConfig load global config file  - ~/.eirctl/config.yaml
 func (cl *Loader) LoadGlobalConfig() (*Config, error) {
 	if cl.homeDir == "" {