would be cool to make another version of that module separatefaces (maybe with a new name speparateparts) which offers 2 more pins:
with the Face Count pin you would specify how many triangles one specific part of the new mesh would have, and with the Faces pin you would select the triangles.
at the end you would want a module which only copies points several times, when they are part of different parts of the mesh.
so you would need to somehow analyze the indices for one part of the mesh.
lets say the face number 0 means index 0…2 of the original mesh.
so in general face x refers to indices (x3…x3+2).
if you now have a list of faces (for one specific part of the new mesh) you would need to analyze the indices referd by the face numbers … (and then somehow build a new point and indexbuffer)
well this sounds very complicated to achieve in a patch. but maybe a plugin could do it very easy (with point and index buffer as in- and outputs).
another solution however would be to copy the points according to these new pins and after that apply the transformations on all points of the new mesh parts at the same time. so the separateparts module would just reorder the indices in a way that it is easy to operate on the parts.
i have that binsize of the iobox in mind to resample transformations in the right way.