This is a novel I've read in the 90's. I have a very dim recollection of most the below, so some of this may be dead wrong.
An operative/secret agent/spy has to complete one or more missions. When faced with a problem, his handler can unlock personas - lover, thief, fighter, etc. However, he does not have a say in unlocking these. He may need to justify or they can decide based on what they see through his eyes?
Toward the end of the novel he assaults an evil lair (industrial complex?) in the wilderness or swamp. His handlers are possibly taken out by someone else but he goes freelance or retires.
At the end of the book, all his abilities/personas are unlocked for his own use (definitely remember this). This may include super human speed due to missing neurons?