I read this novel back in the early 90's. I seem to remember it had a very colorful cover with an image of faces rendered with fairly crude computer graphics. It was an oversized paperback collecting two novels, which was fairly unusual at the time.
The plot involves a secret society of shapeshifters that call themselves "darklings". I forget the specifics, but apparently when normal humans die it sends out a wave of energy that forces them to shapeshift, so they live in the wilderness far away from people. They change into a different human form, retaining the same mass (so if they become shorter, they'll also be heavier) and don't have control over what their new form will look like. A human woman is abducted, raped and beaten almost to death or badly burned (I forget which) by a serial killer, and then abandoned in the wilderness where the darklings find her. They magically heal her, but regenerate her body using the image of the last person she was thinking strongly of, which unfortunately was that of her attacker. Understandably the poor woman is horrified not only to find herself in a male body, but that of the man who almost killed her. She's arrested by police and tries to prove she's not the killer. There's also a plot with the darklings trying not the be discovered, and the killer still going around killing - I don't remember much of the plot from here on in, just the set up.
In the second book collected in it, some sort of psychic contamination is warping the darkling children when they first start learning to shapeshift, I recall vividly that they end up as round lumps of bone and flesh and the adults have to keep using their healing powers to form openings for them to breathe through. I think the villain was a rogue darkling.