I'm hoping for a spell that allows for me, or anyone else, to change any aspect of their body temporarily, simply by imagining it. Just think of what you want to change, and recite the spell.
There should also be a reversal spell to go back to what originally looked like.
Basically, you should be able to change any aspect of your body within reason by imagining it and reciting a spell, and you should be able to undo it with a different spell.
Perhaps this could also work with people. Think about a person and recite the spell to change into them. (Changing your body into the same as theirs, not trading bodies or possessing their body.)
Another idea: make it to where everyone else sees you as your original, unchanged self. You, of course, would be able to experience everything in your changed body. Keep in mind, these changes are reversible.
I ask that if you come up with one, at least test it!
Alright, go for it!