Interesting situation. I must say, I've never heard one like this
before. I have a couple suggestions:

1) Try to solve the problem amicably and get White to apologize and
admit he was playing a bad joke, in return for dropping the serious
punishments.

2) If neither side wants to solve the problem amicably, then I'd have
to side with Black and I don't believe this was an "illegal" move in the
true sense. In my opinion it was changing the position while an
opponent was away from the Board from a losing one to a winning one.
This is clearly a violation of USCF's Code of Ethics in my opinion, so
White doesn't have a leg to stand on if he appeals to USCF in my view.

3) What is the past behavior of these players? Do the players have a
personal grudge against one another? Have they ever played before?

4) My guess is that White was joking around, but this was a foolish and
kind of a mean thing to do, not to mention unethical.

5) Chess will be hurt if White quits because of an incident he was
meaning originally as a joke.

6) Chess will be hurt if White is allowed to get away with this without
even a warning, unless White apologizes to Black.

7) Chess might be hurt in your state regardless of what happens now,
as positions generally tend to harden, if the problems aren't
immediately solved.

I once witnessed an Iowa TD reverse the result of a time forfeiture,
because after the flag had fallen in time pressure, the coach of the
losing player pointed out a line that would have drawn the game. This
convinced the director who had ruled the position was too complicated to
award a ILC claim (the correct ruling), decided that since the coach had
seen the draw that his initial claim should have been to allow the ILC
claim, so he took the win away, and awarded a draw to the player who had
lost on time.

This director was suspended a few years ago for a multitude of reasons,
but I have never witnessed quite as big a *******ization of a USCF rule
as on that day.

Best Regards,

Bruce