Hmm , come to think of it this could be entirely possible , xp packet editing is hard as hell , or at least it seems to be ,but becoming a gm or a vgm and being able to use a command such as /lvlup or something like that sounds better , I mean it's more plausible to create a auto-shouter with a command like /lvlup than say edit xp packets , and a GM or VGM can spawn items and mobs so the 255 be's wouldn't be a problem , come to think of it I remember a trick such as this back when I was playing L2 , a friend of mine (who was a gm) needed my help and the help of others in defeating a raid boss out of curiosity so he gave me a +65535 weapon and spawned a monster and kept ressurecting it and i kept killing it so I would be able to lvl up really really fast , anyway where I'm going at is that with the help of a GM it's very possible to do whatever/whenever you like ingame.
If anyone finds such a thing or has a suspicion of what it's really about I'm all eyes and ears .