Now that Jon knew that he could add clauses after-the-fact and basically reverse wishes, he thought of a lot of things. Some of them did affect others, but ultimately he decided not to. After that, his first thought was to try being a girl, which raised the question of whether he wanted to have a new life where everyone remembered him being one, or whether he wanted everyone to know he suddenly changed.
Then he thought of twins. Of course, if someone was magically turned into two people, they wouldn't be twins if you went by a strict dictionary definition. But it was close enough.
"I wish that some time tomorrow, something would turn me into two girls both of which have my own mind and memories. I wish that everyone except me and Karyn would assume it can't be reversed."