Kitsune in this setting are of the 'mostly human-looking plus fox ears and fluffy tails' variety so no. You can be a kitsune as the lore has them or you can be an anthropomorphic fox but not both.
Hmm, well I do recall a scene where a Kitsune NPC supposedly nearly reverts to / assumes her "bestial form" -- I think it was one of Kiyoko's sex scenes (Play Loud ?) that mentions it, or at least hints at such a possibility, although that seems to be the theme of her sex scenes, they seem to hint at the more animalistic parts of her character design.
Not much to go on, but if anyone could find the specific scene where a Kitsune NPC nearly reverts to or assumes her "bestial form", then that would possibly provide some more clarity on the matter. I do definitely recall seeing such a scene, but again, I don't really know the specifics aside from it definitely being a Female Kitsune NPC.
There's also this listed in the Codex, which I'll refer to via the Wiki:
Kitsune Codex said:
It's said that kitsune can transform themselves into actual bestial foxes, but no one has yet to give a proven account of such.
https://wiki.smutosaur.us/CoC2/index.php?title=Kitsune&oldid=16702#Metaphysical_Nature
See the above link, the first line of the last paragraph.