Variation texture sets

When texturing an asset we often need to create variation textures of the same mesh.
For example an npc with different colour shirts or multiple damage states. 

Right now we need to either save out different files for each or have our changes in the layer stack and turn them on and off, change the texture set name and export.

It would be good to have a "variation" texture set that we could switch out with the main material while working  This could then be listed in the export pop up as well to be included when exporting textures.
That way we could have all the variations in a single project.