Yeah it's a pretty big change to the database as every post you've ever made and every message you've sent (and things like settings, trader ratings, etc) would need to be changed to point to your 'old' user ID, which could create duplicate entries in tables that won't allow it (because your old account still exists and has data linked to it), and it might cane the database and cause table locks while the changes are being applied. That said I think there's an IPB mod to do it but I'd always be a bit dubious about loading something that makes that many changes to critical tables without doing some pretty extensive testing first. Things like your join date can technically be changed quite easily, but changing your ID # (ie 19275) is where the problems start.
So yeah, short version... unlikely, sorry!