Thank you for clarifying your question! However, I guess there may be some misunderstanding regarding the following point:
but anytime a character or object needs a different Path in a different Skin, I need another Path Constraint for the set of bones to refer to.
Path constraints can change the
Target for each skin, so a setup like the one seen in the GIF animation below is possible.
In the example above, SkinA and SkinB contain the same path constraint, but the target paths are circular Path-A and distorted Path-B, respectively.
If you don't want to share the path-constraint's settings (Spacing, Position, Rotate mode, Mix, etc...), you will have to create a new path-constraint for each skin, but if the same settings are fine, there should be no need to create a new one.
If this doesn't seem to solve your problem, please let me know!