If the person has enough knowledge of the .obj format and the .pz3/.cr2 format they can fix it. Compose and CR2Editor would be great tools here.

Like I said earlier, geometry is stored in the .pz3 for any body part that the grouping tool was used on, any meshes in the scene that were imported in, and any props or hair props that were originally created by importing a mesh in. (BTW, the grouping tool can't change a material, but it's great for assigning new materials as well as several other things. I use it a lot, but not on characters I plan to ever distribute.)

Hope this helps.