Quickest way to do it is still a pain in the ass, if your machine’s light on RAM. It will take forever to get anything done, but… Just open the material selector dropdown on the surface (GoreDom only uses diffuse, doesn’t it?) and click on ‘Open Layered Image Editor…’ Then just resize the overlay layer a bit. If the shape isn’t pleasing to you, open the texture in the image editor of your choice and tweak it a bit, then replace the image for that layer with the tweaked one.
Do I do this often? No. It’s a pain in the ass. But, I do it when I have to. (Also, I’m still using DS3, so things may not be in -exactly- the same places, for you.)