The only way I know of to separate the bones of creatures into more stacks, yet still have the game treat them as bone body parts, is thus:
- create new local creature mats, something like Bone_1, Bone_2, Bone_3, ect. with each one using the Bone template.
- Designate new tissues using the new bone mats.
- Create a new body_plan (probably lots of body_plans) for the creature where different body parts (upperbody, lowerbody, arms, legs, hands, ect.) cycle through the different bone tissues.
Then when you butcher the animal, the number of stacks of bones should equal the number of different bone tissues in the creature that have unique material ID's (though they can all be from the same material template), so long as the body parts associated with those bone tissues are large enough to yield a butchering return.
The number of bones in each stack will be dictated by how many different butcherable body parts containing that particular bone tissue exist in the creature.
Its not quite hoops as fuck, but it is still kinda labor intensive. It would be an easy mod to just change the b_detail_plan_default and body_default files to apply these changes to all creatures using the standard templates, but I've found that any changes to body_default disables stockpiling of body parts and remains. Your skins, horns, hooves, bones, ect. will just stick around in your butcher shop until queued by another job in another shop. To avoid stockpiling issues, you would need to create a new body_plan file, and edit each creature to use the new body_plan.
I originally planned to release a mod that did this (splitting creature bone stacks) but I decided it against it because I would either need to mod a bunch of creature raws, which could cause mod conflict, or fuck up the user's stockpiling. If anyone can figure out a way to split bone stacks that is readily compatible with other mods and unobstructive to gameplay, I would tip my hat graciously to them.