I want to modify an existing android application, but I want to have it keep its original signature, or at least its capabilities of auto updating and using Google Play services.
I am aware of Lucky Patcher being able to be used to patch the system to disable signature verification, however, there must be another way. Lucky Patcher itself is also capable of patching installed application's code, without invalidating any checks in any way. How is this achieved?
I have also thought of a custom apk installer, ran as root, that just forces the apk install by bypassing the package manager, but I can't find the low-level install process to execute this.
Is there any good solution to modifying an installed Android application and have it still have access to Google Play Services and the like, without patching the Android system?