Harry, I'm not sure why something you thought of while your character was in a world in which it was impossible shouldn't be permitted when your character reaches a world where it is possible. I would assume that many of these ideas come to you because you are in play, and your character would be able to use such things where he is--if only they worked. So he tries them, and they fail (and remember, there is no possibility of botch on a skill that is curved out--you can hurt yourself if you're relying on something to work that won't, but you can't do any harm by the skill itself going wrong). You've many times had things fail, only to try them again later and have them succeed. So if you find yourself in a world where the psionic or magic things you can do are all easier, wouldn't it make sense for you to try all the things you couldn't do before, to see if they are easier now?
I would object if, for example, you went out to see Harry Potter and the Order of the Phoenix and then said you were going to teach yourself to disapparate the way they do it in the movie (assuming you've never read the book and that my memory is correct that this is the first one to present the idea of disapparation), because at that point you are trying to use an example your character never knew. I would not, however, object to you trying to teleport based on the fact that it's found in Dungeons & Dragons, or even that you think it ought to be possible to do it so you're going to try it, even if you have seen the Harry Potter film, as long as there is good in-game reason for you to attempt such a thing and we're not using as an example a movie you never saw.
I would also raise an eyebrow if you suddenly decided to try something that John Cross did in one of his threads, but as long as there was a valid in-game basis for your character to want to learn such a thing, there's not much good reason to say that he would not have thought of it. After all, I've known of a thousand different teleport skills, magical and psionic, in games, in movies, in fiction, even in the Bible, but when I was in trouble and I needed to get out of there fast, and so started singing "Homeward Bound" as my magical incantation to get me back to my home base in that world, absolutely nothing in my "out of character" knowledge or experience should have prevented me from coming up with that idea at that moment.
--M. J. Young