In my story, there are two mages. Both are able to change the mind and the appearance of people, including themselfs. The 'good' mage didn't like his former life and put himself into a more likable life, including a new appearance and adjustments of the minds of the people around him, so they don't notice the change. His new life is an average life, but he likes it so much more than his former life.
The 'bad' mage finds out about this and now coerces the good mage to do his dirty work with his magic, otherwise the bad mage will revert the changes and the people will notice what happened. The good mage is so afraid of this, that he complies and works for the bad mage.
Which restriction can I put on the magic of both so that the threat is effective enough? Otherwise the good mage could just revert the reversal and it would be an endless back and forth. Both mages are equally strong regarding their magic and it's no option for me to say that these changes can only be made once. Also neither one can be completely immune to the other one's magic.