I’m wondering if you can flip a bone deformer without the character attached to it messing up.
Yes, you can. Just go into Setup Mode and the deformer will turn red. Then set it up or adjust it however you want. Before leaving Setup Mode you must now copy this new setup by selecting the Deformer module either in the Timeline or Network view and hitting the Copy Resting Position to Current. Once you’ve done that you can leave Setup Mode and your deformer should be at it’s new position.