Assembly Custom Property linked to Part Custom Property

I'm working on creating master assemblies for my company that will be renamed and the parts contained inside will be renamed. I currently have a custom property that is holding the material of one of the parts. The problem is, when I rename that part, it breaks that link. Is there a way to link it differently? Is there a generic property? Right now it says something to the effect of "SW-Material@extWallSkin.SLDPRT", but when I change the file name of that part, it doesn't carry over anymore. If this doesn't work, I guess it will have to be a manual custom property that the designer fills out, but I was trying to avoid that. Below are the three custom properties I'm trying to make work.

SolidworksAssemblies