Oh, that's right. Well, I guess what I'd do is this:
1) Move the players back to their post-trade teams
2) Allow those teams to make the corresponding trade in reverse (with a reverse loan, etc)
Since Commissioners can edit pretty much anything else, I don't see why they should not be allowed to edit loans. However, that feature will probably be a few months out, so I would reverse the trade in the way I stated above for now.