What program did you use to edit Undead bone size?
I used no program to edit it. When WoW was originally released undeads had larger shoulder size. The last undead model to still have big shoulder is from patch 1.1 iirc and .m2 has not changed throughout entire vanilla. So all I had to do was grab undead model from patch 1.1 and make a custom patch for it.
You don't want the release version of undead model, since it lacks cannibalize animation (it was added in later patch.)
I don't suggest porting the model that my patch contains to other expansions, since it will lack certain animations added in later expansions. So if you are to make a big undead shoulder patch for another expansion you would have to edit shoulder bone of the undead model, iirc you have to edit the size of shoulder attachment bone.