Hello there. This is a minor mod that adds additional internal skins to all standard vertebrate creatures, causing them to yield more leather upon butchering. The number of skins obtaining varies depending on the creature size, but follows this approximate scale.

Body Size / # of leathers
1900 / 1 leather
19000 / 2 leather
49000 / 3 leather
212500 / 4 leather
425000 / 5 leather
850000 / 6 leather
1700000+ / 7 leather

This is achieved by adding additional skin materials to the body_detail_plans, additional tissues to use those new materials, and new small internal body parts using the new tissues. Upon butchering, provided the creature is large enough, the new organs will yield skin tissue that will be tanned into additional leather. The tissue of these new organs is shaped as FEATHERS to minimize interaction with combat.

Unfortunately, it does modify core raws (this is something I try to avoid in my mods), so it could conflict with other mods that also modify those raws. Specifically, b_detail_plan_default.txt, body_default.txt, and (and this is the big pain) material_template_default.txt are altered slightly. If you currently run mods that also interact with these files you might experience some conflict.

Interesting side note, because of the changes in this mod, scaled vertebrates, such as cave crocodiles, will now yield leather as well.