The files that tell the game how to change the sim's face, hair, and makeup are a set of unlabeled .simo files. I've extracted all the files that have werewolf teeth, body hair, et cetera, and poked at them a bit. Just taking the original .simo files and removing the face parts resets the face to 0 sliders all around, but making a new outfit with CmarNYC's Outfitter results in a werewolf transformation that leaves the facial sliders unchanged so one can easily make a werewolf form that still resembles the original sim.
Right now I've got one which applies the claws, teeth, and a set of contacts I made, but leaves sims otherwise unchanged.

It seems to apply correctly in cas and on random sims that have been changed into werewolves, but it could use more testing!

Couple other notes-
Outfitter crashed when I tried to add the original body hair, but it should be possible to add some other accessory and makeup that paints body hair on the sim. I'm thinking of making the final version add gray hair like that and camkitty's wolf tail as bracelet, but right now I want to make sure the override works properly to begin with.
I initially missed a couple of the TF files, but I'm pretty sure I've found them all now.
Since the original werewolf transformation leaves custom sliders unchanged, there should be a way to edit the transformation's face data so it only adds pointed ears, a snarl, digitigrade legs, things like that, but I haven't cracked it yet.

I've attached the werewolf transformation replacement as it stands now (WereTransformEyesFangsClawsOnlyContact.package), which includes the contacts that I made for it. Supernatural is required for this to do anything (although people without supernatural can still use the contacts), but nothing else is needed. I've also added a package (OriginalWerewolfTransformationSimO.package) containing the original files I extracted for reference.