How to darken mansionbase walls

[Reminiscity]

Copy all the mansion base files and create place them in another folder. (Just so you won't mess up the original files) Open up the .dds file and edit whatever you want. (Darken, add textures, w/e)

I've tried that and nothing changes . There must be more to do than that? like changing a line of code in one of the dae files or something?