Okay I've decided to extend my AppleCare warranty. Found some guy in my country who's selling just the code for a cheap price with no box; couple of people bought from him too and had no problems. Anyway we're going to do a meet-up at a shopping centre, register the warranty, then I'll pay him in cash. I'm thinking that everything should be fine if it's able to register with Apple, right? Can anything go wrong after that, like say, Apple decides to revoke the warranty for some reason?