I just recently got engaged around christmas time and pretty much thought we had all of our wedding party figured out.. well we were wrong. My bff is my maid of honor and my fiance decided to have her fiance as his best man. well he feels that there isnt a friendship between them anymore and wants to make his other friend who is a groomsman the best man. the groomsmans wife is also in the wedding as a bridesmaid. I wouldnt mind her as my MOH but i am closer with my current MOH. WHAT TO DO!?! I read a few places that i could opt to not have anyone specified as a MOH or BM but i really.. really dont want to hurt anyones feelings. I just think we rushed into choosing who is in our wedding and our wedding isnt until 2012 :(
There's no reason to change your MOH to "match" up with your FH's decision to change his best man. Keep your bff where she is. It will hurt her (rightly so) and there's no wedding rule that the best man and the MOH need to be a couple.
You didn't ask for advice on your FH's decision, but unless he's prepared for his friendship with his current best man ending completely, he may be better off just leaving things as they are. I take it he's already told the best man he's the best man?
And you're right, this is why it's a good idea to wait until closer to the wedding to pick your wedding party. Friendships can and do change. But maybe another bride will learn from your situation. Good luck!
You don't need to and shouldn't change them unless they've done something really terrible to you or your FH. Their duties include showing up to the ceremony appropriately dressed and acting as witnesses. It really doesn't matter what titles go to whom.
ETA: You can't change their titles without hurting them, unless they volunteer to step down.