It's server hacks, there are some released here:
https://www.mpgh.net/forum/404-call-d...33-update.html
https://www.mpgh.net/forum/404-call-d...ol-v1-3-a.html
https://www.mpgh.net/forum/404-call-d...ns-v1-5-a.html
Not all of the server control hacks can change the XP, but they have plenty of other fun functions.
Does this answer your question?