I literally just thought of this earlier. Idk if that'd be an option because it seems these textures have height, bump and normal maps associated with them. Unless it's in one of the resource files that can be imported? I havent seen much though in the xmls.
I'll look more into this tonight and get back to this post in the morning
edit: Yep, they're in with the assets. We'll have to wait for the dev to allow mod support for that.
Perhaps you could get your results with SDX and Unity Asset Tool. It's above my head but if you're dedicated enough, I'm sure you'll understand it