I did something similar with a guy that had high patience rating a few seasons ago. Up until then, everyone I demoted that had a patience rating above 85 didn't take a demotion ratings hit. However, I demoted a guy from AAA to double AA because my double A team was playoff bound and my AAA team was not going to make the playoffs. So, I figured I would demote the guy to AA, play him in the playoffs, then promote him at the end of the season for an extra ratings bump.
Nope -- he took a huge ratings hit with the initial demotion and didn't gain back those ratings. I no longer play that game.