This makes me wonder, do tougher skinned creatures make more protective leather?
Depends what you mean by "tougher skinned," I guess. Since the material properties for skin and leather are seperate, merely changing the skin's material properties won't affect the leather. As for making the creature have thicker skin tissue... dunno, I kinda doubt it would make the leather armor tougher, but that's just a guess.
I'm aware of how to do that for every other tissue, but isn't leather directly produced from skin? Hmm, wait that means you can directly edit a creature's leather material in the raws at the "load standard materials" tag? I could have sworn I read that wasn't possible, but maybe I misread it for "this isn't done in vanilla DF".
In the creature raws, after the Body Detail Plan tag that loads the standard materials (and before the one for tissues to be on the safe side), you can use the [SELECT_MATERIAL:BONE] tag (and a similar one for LEATHER, and also SKIN if you want, which can give the creature skin of titanium or brittle as a biscuit if you're not careful with the numbers). Immediately after the tag, simply put in the material properties you want to change. For example:
other tags other tags other tags
[SELECT_MATERIAL_SKIN]
[MATERIAL_VALUE:2]
[IMPACT_YIELD:20000]
[HEATDAM_POINT:12000]
[SELECT_MATERIAL_LEATHER]
[MATERIAL_VALUE:2]
[IMPACT_YIELD:20000]
[HEATDAM_POINT:12000]
other tags other tags
Or whatever. Whatever tags you put will overwrite the default ones. Tabbing is optional, it's just an organizational aid. There's a tag in the default skin material and the tanning reaction that lets the game know that Creature x's Skin Material + Tanning = Creature X's Leather Material, so there shouldn't be a problem in getting the creature's super-leather from the super skin.
If you're doing this for a lot of creatures, it might be better to just make the template and mess around with that, but it's a bit more complicated and it's two minutes to midnight and I'm getting tired so I won't explain unless you really want me to, and not until tomorrow.[/code]