Reddit reviews Changeling (Shadowrun)

Try Changeling, it might be what you're looking for.

Allow me to recommend Changeling by Chris Kubasik. Gives you some perspective on 2050's era Shadowrun from the perspective of a guy who mutates from a teenager to a troll. Great plot and interesting characters.

You could always try the Shadowrun novelizations. They're mostly garbage, of course, but I remember liking this one about a gifted teenager who goblinizes into a troll.

Found it: Changeling.