CollapseSubObjectMaterial

"Takes an object that has a multi/subobject material - and collapses the material to use only the subobject materials that are assigned to face IDs on the object. Modifies the object as well - consolidation material IDs and collapsing it to an editable mesh. Great for cleaning up nasty subobject materials on characters or buildings that have been attached several billion times.
v 1.20 Added ability to reduce nested submaterials - as in - get rid of submaterials that exist inside of sub materials. Original idea and code from Brett Hartshorn.
version 1.21 Added a warning label so the user realizes collapsing material will also collapse the modifier stack of the object."