I have an old iPad my son is using (iOS 9) He plays clash of clans, we changed the Apple id to his own but the Game Center ID is still mine. If I sign out of Game Center and sign in with his ID will I lose all his progress in Clash of Clans?
Well it depends on how you want to play the game. If you just want to play the game locally on one device it shouldn't make a difference if the progress and data is stored on-device.
Whereas if your progress is stored using game centre then the progress will be reset.