You flick your wand one last time, making it so that the whole world besides them will remember them as being the gender-switched cat-people they are. After all, you can't just leave them with no legal identity. They're going to have enough to worry about just adjusting to life in their new forms without having to find new jobs or reaffirm their citizenship or any other such things. This last change complete, you flit off into the night, giggling to yourself.