Off to Be the Wizard, Paperback/Scott Meyer

An io9 Can't Miss Science Fiction and Fantasy title in March 2014. Martin Banks is just a normal guy who has made an abnormal discovery: he can manipulate reality, thanks to reality being nothing more than a computer program. With every use of this ability, though, Martin finds his little -tweaks- have not escaped notice. Rather than face prosecution, he decides instead to travel back in time to the Middle Ages and pose as a wizard. What could possibly go wrong? An American hacker in King Arthur's court, Martin must now train to become a full-fledged master of his powers, discover the truth behind the ancient wizard Merlin...and not, y'know, die or anything.