It *is* a poor design, & I'm not aware of any easy fix for it. Probably too late for you now, but I think the best way to avoid the problem is to leave the bolts that screw the muffler to the hanger well alone. Instead buy a pair of hangers for the new mufflers & when removing mufflers in future, unbolt the hanger from the frame, still attached to the muffler.
regards
Ian.
