I read a story once about a man who went to another planet and had himself modifed - He could see in the dark, grew claws, was super strong and super fast. He was normal otherwise until he needed to modify himself and then he could stay in that state for only so long because of the metabolic demands on his body. Then he would have to change back to normal, or be forced to, and sleep and eat alot of calories to replace what he burned.
He was a prospector with a friend and I believe they found a ring that when he put it on it modifed him even further and helped him stay in that state for longer periods of time, with a shorter recycle. He was trying to trace where the ring came from. - or I might have 2 stories mixed at this point.
One part I remember is: When he was captured and tied up, he modifed to escape. One of his captors (government agent??) was also a modifed person and a big battle ensued. Of course he won and got away. He was very surprised because being a modified person, was either very expensive or/and against the law, so you didn't meet up with other modifieds very often, if ever.
This was read about 25 years ago and I believe the story was older than that. I met a girl that was an avid scifi reader and she and her mom had 100's of scifi books. and, no, I can't ask her, it didn't work out.