Much the same as you can currently do in Poser with any figure using Python?

texvertex = poser.Scene().CurrentActor().Geometry().TexVertices(index)
texvertex.SetU(value)
texvertex.SetV(value)

Alternatively, and this may prove to be very much easier, simply swap the geometry using the method shown in the Poser 2 figures. Yes this has been available since Poser 2.

Search Buisiness Man P2.cr2 for "alternateGeom" and "geomChan" for the required lines.

Poser library files have always been text based so it is very easy to get into them and tinker.