We just don't. Idioms have historical origins that don't always translate. "Play nice" isn't an idiom that translates with any other word combinations. You cannot say "Run Nice" or "Shop Nice" or "Eat Nice" and have the same meaning. "Play nice" means don't cheat (basically)... "Run Nice" doesn't mean "Run nicely" or "Run fairly." It just doesn't translate at all. Just like how you can't change the verb in "play nice," you also can't change any other aspect of the phrase, without ruining the whole phrase. So again, we just don't.