You could spawn different invisible meshes with a different physical material.
It shouldn’t affect FPS much either being they don’t render.
Because the target environment is probably mobile, you would/should benchmark this with 100 invisible meshes and see if it causes any bad effects prior to implementing it properly. Since that’s likely never going to happen after you make the system properly, benchmarking it like this would give you a decent idea of what you can expect performance loss wise.
Another option may be spawning decals. You might want to do that anyway for things like oil patches maybe?
Anything that has a material can have 1 phisical material assigned to it…
Ofc, you could also properly UV and get multiple materials on the mesh, but you wouldn’t get any blending.