So I’m in a bit of a unique position in that my UVs are completely procedural. So here’s a screenshot of the rocks, but they’re not incredibly interesting. I did figure out how to save separate UV maps for the colour and for the paint strokes though. Each paint stroke has slightly varied colour, but each stroke is a solid colour so I can get away with a super low resolution. And then I can make a version of the paint strokes with all 5 variants and set the UVs for each paint stroke to only cover one random stroke.

From the non-destructive version of the models with the geometry nodes modifiers, I made a Python script that bakes everything to textures and an FBX file, and a script that generates Unity materials using my custom shader based on the names of the materials in the model. I can then automatically link these materials to the model in Unity for easy importing.