"While I sort of agree Fazzel  - it is totally possible to make the modification within Poser and leave it there - it is only a temporary change.  The prop or figure will be saved with the new/changed material zone and the geometry in memory will reflects the change while Poser is running.  One must wonder if you save a figure to the library with altered material zones, how does Poser restore these on next use?  Does it, horridly and probably, store the entire Figure geometry in the CR2?  There is no other way to make the change permanent without change to the geometry definition (period - end of argument).  It may not be the original geometry definition (the original .obj file referenced) - but there must be a new one somewhere to relay the change in name or configuration.  Of this, I am well experienced and confident. :)"

Almost but not quite...:-))

If you save a character to the library, then if (and only if) the changes would affect the original .obj, then Poser creates a new .obj in the same library. The corresponding .cr2 file points to the new .obj....

At least, that's what I assume, due to the fact that my Character library has a few .obj files in it (that I didn't put there), where I'd changed something that would have affected the original .obj. and then saved the figure back into the library.

I've just tried a quickie experiment. I loaded Posette, used the grouping tool to create a (random) material zone, then saved the CR2 back into the same figures library (under a new name, of course).
Sure enough, when I looked using Explorer, there were 3 new files: the .cr2, the .png and a .obj.
All in the character folder/directory.

So that would seem to explain how Poser does it.

However, none of this gets to the gist of the problem - how to remove and/or rename material gruops within Poser.
Personally, I don't think it can be done. I'd love to be proved wrong..:-))

Cheers,
Diolma