My use case was running my service after mglaman\PHPStanDrupal\Reflection\EntityFieldsViaMagicReflectionExtension (and before others), I guess @mglaman's idea was running the same service after PHPStan\Reflection\Annotations\AnnotationsPropertiesClassReflectionExtension (instead of before, that is the current order) so the code in EntityFieldsViaMagicReflectionExtension could be simplified.

Maybe service decoration could be the cheap answer for this use case too...

My suggestion is:

1. Get in contact with phpstan-drupal maintainer, agree on what EntityFieldsViaMagicReflectionExtension should do, so that you don't have this need, and the extension is useful for everyone, OR:
2. Contribute a new configuration parameter to phpstan-drupal that conditionally turns off EntityFieldsViaMagicReflectionExtension so that you can register your own extension in its place.