Creating & distributing a modified version of xbtit is fine as long as you stick to your own hacks or hacks have been released on the
open source forums. The moment you add a hack that hasn't been released to Open Source by either the hack author or Lupin you are breaching copyright laws.
We will be lodging a formal complaint to sourceforge about Cyberfun's inclusion of the Invitation hack on the grounds of Copyright Violation which is prohibited by their
Terms of Use.
If you plan to release your own modified version then you'd be wise to stick to including only open source hacks. I'm not trying to discourage you, Creating your own version is a good thing as long as you stick to the Open Source material.
However kickass is right, anyone can add hacks to xbtit so unless you know what you're doing and have the ability to rewrite the code to optimise it and reuse pre-existing queries rather than just creating more queries like most hacks do then you'll just end up with something that runs very slowly the moment you have more than a few users browsing the site.