Rules for the phone app:
1 The phone can only change one aspect at a time.
2 Anyone can use the app if they have access to the protagonist's phone.
3 Both mental and physical changes can be applied.
4 Changes can be undone.
5 People may or may not notice the changes, but this is not reality warping. It cannot change the history of the individual that the changes are applied to.
6 Have fun, no change is too off the wall.