Hi, don't think it's an issue to leave the posts under a nick that is not in use anymore. You can always answer with your "new" nick.
Anyway, I'm a bit puzzled.. you say you lost your "5" password but you're asking to move the posts from "4" to "5"... supposing that this would be possible, of which I doubt, what's the point of doing so?
Il mago Oronzo mi fa un baffo