The answer, then, is to have a single "store" app with multiple sources, such that you can add and remove sources at will. This is exactly what F-Droid is able

The answer, then, is to have a single "store" app with multiple sources, such that you can add and remove sources at will. This is exactly what F-Droid is able to do on Android, and what nearly all reasonably-popular Linux distributions have been able to do for decades.