i have finally learned enough to make plantigrade edits for avatar bases
also bringing patch files to vrchat avatar edits (at least i haven't seen used anywhere else?)
i've put it up as pay what you want / free on gumroad here https://pinballswizard.gumroad.com/l/BigCatsPlantigrade
biggest shoutout to @Razra first and foremost from whom i have learned this dark art, and who listened to me complain about issues as i ran into them and gave me pointers on how to fix them
slowly learning more as i fiddle with blender and unity, this is the sort of change i typically want to make to many avatars because i just find digitigrade bad with full body
fun things learned this time around involved ways to add more geometry to the mesh without editing the existing UV map (thanks poke faces), and more ways to manage weight painting
perhaps more technically interesting for this was choosing to use patch files to distribute it, there have been issues in the VRCFaceTracking community with an author of base edits for face tracking having their ko-fi store taken down because they included an original fbx with their modifications
instead i've gone the route rom hackers and fan translators have been going for decades now with a patch file, i with the bps format because there's a handy online tool that supports it, and after running through all the options it seemed like the best option that would not include the original base author's content while applying my modifications as a patch
of course a binary diff on an fbx exported by two different versions of blender still produces a large patch file, but it's still not possible to extract the original fbx or the edited fbx without having the original already, which neatly solves concerns of distributing a paid for asset for free. (i did also contact skip4d and got their blessing, regardless!)
it complicates the process of actually installing the modified fbx, but i've provided detailed instructions on gumroad once someone actually grabs the content. mostly it boils down to importing an fbx, setting the correct rig, then using a community tool to copy over existing components like the avatar descriptor
all in all i'm glad to have made it, glad for the experience writing it all up to distribute more widely, and i suppose we'll see if anyone cares enough to grab it over time. i know the friend i made it for loves it, at least :3