[LadyLightning]

I'd think that perhaps a weapon which has all of its part slots filled with custom
parts made of the same material should have its material bonus changed to
that material.

Example:

1.) Get a Rockdirt Wo Dao
2.) Install a blade, guard and hilt, all made of coral.
3.) Rockdirt Wo Dao becomes Coral Wo Dao instead.
4.) Remove the coral razor blade.
5.) Wo Dao becomes Rockdirt again.

It makes no sense for an entire weapon's worth of parts to be replaced, but
its material doesn't change. This could also be a way to make more dungeon
drops useful, as you could simply replace the material type with custom parts.