I don't know hexagon; but is it possible to make your groupings without extracting?
Seems like an extra step in there...Extract (breaking the verts apart), then weld (putting them back together).
The groupings; AFAIK, are based on Material assignments; at least they are for what I render w/. Whether the groups are part of the same mesh or not is unimportant. Groups can span several objects and/or several groups can share the same object.
I usually go with welded mesh for 'organic' objects that need to have smooth transitions in the mesh and seperate objects where there needs to be a 'hard edge' between meshes. Might be different in Poser.

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