I'm doing PatchLauncher, a program that takes binary patches and applies them to a copy of UnrealTournament.exe before running it. These patches are generated by GNU diff (which means the launcher comes with patch), and it's based either on a decompiled version of the Unreal virtual machine, or on the public headers.
#2. Why are you going to do that?
While there is already a multitude of ways to extend Unreal and it's multiplayer brother, I've always found it rather difficult to make significant changes, especially with total conversions (like those out for Doom). Of course, there is Legacy (I've got to hear about it thanks to a trusted source called EvilGrins), and other attempts, but I still want to make a real game, even if it is just a giant extension for UT that uses custom Engine stuff.
#3. What have you done yet?
Just this sketch for how it would work.
No, really. I need your help to build up some concept on patching The Engine, before I can move on and do anything in real C++.