TEMPLATE_PLACEHOLDER define problem

[softwarecrash]

Hello,
i try to redefine the template placeholder with

#ifdef  TEMPLATE_PLACEHOLDER
   #undef  TEMPLATE_PLACEHOLDER
#endif
#define TEMPLATE_PLACEHOLDER '`' 

#include <ESPAsyncWebServer.h>
.....

but it was ignored, so when i change the line 63 in webResponseImpl.h to the new character it work.
so what can i do to overwrite the default template placeholder without modify the library direct?