Attached Link: http://koti.mbnet.fi/~ilaripih/MPEHome/MPE3_beta/Tutorials/Description/materials_description.htm

In MPE's Materials tab, select the materials you don't want to be affected and click "Delete". Note that this doesn't remove the materials from you figure, just from the MAT pose. Materials that aren't referenced in the pose won't change on the figure. See section 6 in the linked tutorial.