I just found out that [cutting model in half > unwrap > mirror geo] works. Will this case a problem in the future? I suspected it is an overlapping uv?
Indeed it was the idea. I went with near future and use of advanced prosthethics to allow for greater speed in the game. Someday someone will make one :P
Transfer Attributes is the tool you are asking for. But for future projects, I recommend that you get used to using instances. Edit > Duplicate Special (optionbox)