If you are in a tournament and you want to change your rank, you must withdraw from the tournament first.
If you are in a ladder and you want to change your rank, you must withdraw from the ladder first.
If you are in the middle of a rated game and you want to change your rank, you must resign the game first.
I should not lose an opportunity to gain rating points and rank because my opponent is in a tough spot and has an ego attachment to his rank.
How does this sound?
I guess the protection we put in place here is that it resets your provisional status.
We had a system in place before with ladders that forced you to withdraw from ladders if you changed your rank and we got a lot of negative feedback from it.
I wonder if we shouldn’t just gray out the option to change their rank if they are in a tournament?
Have you had this happen more than once SunPin?
Damned if you do, damned if you don’t. 
There has to be a solution.
Maybe allow the player to change his rank and in all existing games, the opponent doesn’t lose the ability to gain rating points and maybe even not lose rating points whereas the player who changed doesn’t gain and is committed to possibly losing points based on his previous rank.
You only need to be robbed once to become a lunatic activist against robbery.
I’m aware of once. This may have happened a few times and would explain while, in all my title tournaments of losing rank, there are other players who have lost as many games but still retain their ranking.
Your solution to tournament ranked changes is elegant and pythonic.