It affects brick rendering so Badspot would have to implement this in the engine, it's impossible to change with scripts.
Idea: Have the engine make all bricks with this fx paint use a special "blank" texture when rendering instead of the TEX:BRICKSIDE ones. This would leave the studs/bottom parts of bricks, prints and the grainy part of ramps, but allow for 'smooth' walls.
I like this idea.