8 XXX : transformation

Two words : Have. Fun. After all, if I can change myself at will with that app, I can also change myself back, and thus I'd get to experiment with what seems fun. Of course, I'd also change others, I'd still try to make it right for them, and not completely overwrite their personalities. Unless they're REAL assholes, but for them I'd be trying to replace them with nicer persons.
Change gender and reality (basically obliviate myself from everyones' memories). Start a business changing the genders of trans people so they no longer feel dysphoria (with a 30 day return policy just in case obv). Side business where I turn furries into their sonas for a limited time and we use the reality feature to begin voring the rich.
In a fantasy, I would go sadistically transform people into degrading forms forever. In real life, I would hire a lawyer to find out how I can obtain legal informed consent and then make a business transforming people into whatever they want.