Thank you for your interest! The first few lines of code contain some variables to tweak the behavior. I spitballed some numbers there. I'm generally opposed to offloading everything to mod-settings as that creates clutter.
Keep in mind that the scarring effect is progressive. Tiles can be selected multiple times and the change will be more dramatic after multiple visits. I use a curve to bias most of the scars close to the ore in question that was depleted.
Decals certainly would be a nice touch, but that's significantly more graphical work. I am not fond of the biter decals and I would rather not re-use them, particularly because they already are used in a different context, but new decals are a possibility if the graphics were provided.