Meshes and weights

Hypothetical situation…no, actually it’s real…

I have a model that I’ve made changes to one side (the left arm), modifying the appearance a bit, and added a new set of vertices between to others. I did the copy/flip thingie, but then realized something - If I reassign all the weight groups, I lose the special adjustments that were made to make the elbow joint work correctly. I know this is a long shot, but is there any way to do this without manually having to re-do all the weights (and I don’t mean just assigning the weights, I mean the physical trial-and-error process of weightpainting and adjusting)?

here’s something which I think could work. First, copy the arm and mirror it. Then, separate it from the other part of the body (Pkey). Then, enter edit mode for that arm, and rename all the vertex groups to what they should be (hand.r to hand.l for example). Then, join it back with the rest. If all works like it think it should, the vertex group should stay changed, and be added to the list of the others (if they don’t exist already).

Martin