The modern WWE performer probably enters the flagship arena with a certain, relative confidence. The days of complete repackages are over, for now.
You're probably going to be the same person you were in NXT. Well, only without a long-term character arc, or the creative freedom to do more than endure interminable chinlocks, or a fandom given a reason to give a sh*t about you, or the opportunity to actually get over on a major show presented in front of an awake and alert audience. You might become the most parodic version of yourself, defined entirely by one characteristic. Emma became Pointy Dancing Hands, Tye Dillinger became simply Pointy Hands, and virtually everybody else became merely good little hands in the Lenny from Of Mice and Men hands of Vince McMahon.
But the worst thing that can happen to you - beyond entering a bottleneck of 50/50 booking, or simply not appearing much at all, like SAnitY, or being drafted to Main Event - is a simple name change. Yes, you might lose your first name. You might become a meme. People might never take you seriously ever again.
Still, Vince McMahon probably won't turn you into a chicken man.