Quote - "can you then use those to replace the originals, so they are loaded, instead of the originals?

Yes.  Just re-save the tree as a new species with the new mats to another folder.  Then you can just load them in anytime you want and they will contain the new mats."

Ok, so change the mats, resaved them as new trees, and replace the original tree files with these new ones, properly renamed?

Just wanna make sure I get it right befor mucking about.

Way too many people take way too many things way too seriously.