currently the repair tool is only for manually built walls. that said you could cover it up with a custom poster made to look like the wall (either a screenshot of a clean portion or just a solid color that is the right color) but i think custom items cause lag if theres too many so its up to you if its worth it or not. im hoping eventually he adds the option to fix those and a number of other things around the base as well as cleaning more things (like the bedroom carpet and the breakroom floor, and the nasty stains around the vents, just as a few examples)
There is a mod you can use that changes the textures: CleanBase by acitulen. I don't know if it works on the latest version but it be worth taking a look at.
