I read this in the early 1990s when I was a teenager and I have no idea whether it was old or new at the time.
Changing your body involves going in to a tank of liquid. People wear bodies of many and various different types (probably chosen mainly for fashion reasons) but certain body types are prohibited although I don't really remember any of the reasons why.
The main character is persuaded by someone to change his body to an illegal type. Perhaps he becomes involved in some kind of secret underground organization. The new body is of a type that he has never seen before. The main thing that I remember about it is that it has a panel of lights built into the chest and after he has learned how to he is able to communicate with other people in bodies of this type at incredible speed by flashing these lights.
I've spent considerable time web searching with no joy whatsoever. I'd love to re-read this book... the image of the flashing-chest-array communication has been stuck in my head ever since I read it but I can't remember whether anything else about it was noteworthy.