textures – How to create a modular enviroenment that doesn’t repeat itself?

I am creating a modular environment for a game so I have walls repeating quite often. What I want to achieve is to have the same walls with a different look, even though they are the same mesh sharing the same UV map. I took a screenshot of what I would like to achieve, the same walls repeating but with different stains across them. I should specify that I dont’ want to use unique materials but only tileable materials for optimization reasons.

enter image description here

I thought of using decals but i don’t like them too much, is there an alternative?