You really need a modelling tool to do what you want to accomplish instead, but that's a pricey solution. I believe modo (which DAZ uses to make their characters) has background morphing and reversing morphs back out, which would do as you want.

However, it's probably better to just redo your fixes properly... separate fixes for each side on your character, then use the property editor to control both and save as an ERC freeze... Which you would see if you study the characters a bit closer.