From what I can remember, someone invents a process on Earth, "present time", whereby a person can be transformed into their "true" selves. The first to undergo the process, which I think takes about a month, are a man and a woman. The man turns into a small flying fairy-like being, and the woman into a Amazon. Others want to undergo the process, but at first just assume that all men will become fairies, and women will become huge muscular Amazons. They "discover" that the process is unique to each individual that tries it, each becoming their true selves. Many are transformed in the book. I think a transvestite became a woman, and others into creatures of all sorts. The book may have been called *Changling(? Transformation? Transformations?