Sadly, I cannot seem to find any surviving internet mirrors of my old Lamarckian Shapeshifting system for Amber, and I don't seem to have it as a file on this computer. It may be lost forever.
Bounded in a nutshell, the system was roughly that each lineage or house of chaos had developed it's own unique version of shapeshifting. I think they were dirt cheap, like 5 or 15 points. They gave you access to forms related to the themes of your House. Bullheaded desire (and a few points) could broaden this for you and future generations.
So if you were from a House of trackers and investigators, you'd have forms based on bloodhounds and stealthy ambush predators. Possibly extra sensory organs.
A sorcerous house might draw from familiars and ephemeral pixie forms, perhaps with a tendency to multi-limbed and large-brained bodies.
Each House's version of shapeshifting resulted in a unique pool of forms to be taken, along with the ocassional minor power, if memory serves correctly. But you couldn't mimic a specific individual, couldn't knit-closed wounds, and only the House of Barimen could take a wholly human form.
For that campaign, we (for my co-GM also crafted several houses, and the players filled in some holes) worked up a complex of web of 20+ houses, each with their own specialties. A nice benefit was all the flavor it gave to the courts of chaos.
This was a limited-Logrus universe, but would have worked even better in a logrusless setting.