There has not been a lot of progress this week, partly because I felt quite inspired by Sunday's roleplaying game and ended up working on character portraits instead,
I did the scars as a bump map using bpainter. Then figured out how to string normal and bump nodes so that everything would go in nicely.
Normal map texture colour out plugs in to colour in of normal map node. Normal socket out of normal map node plugs into normal in of bump map node.
Scar image texture colour out plugs in to height in of bump map node and alpha out plugs into strength in. Normal out of bump node goes into normal in of another bump node if chaining more on or into normal in of the principled bsdf shader.