Add vertex groups to objects

I've been trying to turn an object with three textures (which I believe was a bookcase, made by radioactivedotcom) into a stove. I started by cloning the object in question, then cloned a stove to get its Rig. I changed the tuning of the bookcase through the Tuning tab, then imported the Rig binary file from the stove. The mesh is already weighted and with cut numbers, but every time I try to import it to the .package file I get the "mesh with a vertex group not part of the mesh that you're replacing" error.

So is using a mesh with different vertex groups to the ones in the cloned object possible?
Thanks a lot in advance