Cody. Perfect name for a former rodeo cowboy. Actually, I liked the name so much, I had people calling me that in 1989, instead of Bill, which is my legal first name. My wife and her family only knows me as "Cody". When I was employed, I'd sign all Purchase Orders as "Cody".
Anybody can have a nickname and use it, but in order to change the last name, a person has to go before a Judge and explain why you want your last name changed.