Previous to poser 6 if you had props that you don't expect users to parent to a figure you simply provided a pp2 prop file for each material option. after all prop files are not very large unless they have a lot of morphs. with poser 6 Efronteers finally added a multiple material file that will work on all content, its the material collection, and you can save and load them in the material room.  You can also convert a mat pose to a material collection fairly easily with a text editor, and I believe that EF included a python script which converted mat poses to material collections.