It is possible to texture paint with Blender 2.8 with layers and in this video I show you how to do this.
Very nice Thank you ,
Do you have tutorials about exporting this texture with decals ?
Good to know this can be done without a plugin. A little more awkward, but if it works, it works.
One question: do you have to duplicate the whole principled shader? Or can you duplicate higher in the chain, maybe at the actual image map?