Thanks to Igor Djordjevic who brought this to my attention.
To undo AppManfest (restore the default manifest) you have to force the IDE to regenerate the default resource file. And you can achieve this by following these steps:
- delete the external application manifest which AppManifest has added it (Application.exe. manifest).
- delete the default resource file (Application.res).
-if the project is already opened in the IDE, close it and reopen it again, the IDE will inform you that it needs to recreate the default resource file. Let it create this resource file.
-from the project property, check to enable (Enable runtime themes) option.
-rebuild the project. The default manifest is now restored.
-maybe you need to close and reopen the project to see the themes result at design time.
So, this is the way to undo AppManifest.