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Can one create joints that affect only one of two connected body parts? If the original mesh is welded, and poser splits the weld internally, is it possible to make joints that move just the vertex that is belonging to either the parent/child? I thought for scaling this might be possible, wasnt sure though.

If you remove the child's joint affectors from the parent's listing, in the .cr2, you can prevent the child from deforming the parent at a joint.  I've never examined such a case specifically to see how the weld seam is affected. 

You could also set up a joint using the falloff zones, then position the zones in a way that prevents one of the actors from being affected by the joint. 

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Cage can be an opinionated jerk who posts without thinking.  He apologizes for this.  He's honestly not trying to be a turkeyhead.

Cage had some freebies, compatible with Poser 11 and below.  His Python scripts were saved at archive.org, along with the rest of the Morphography site, where they were hosted.