Yea all the good stuff is wrapped up in unreal editor files which are under 2 layers of compression. You can totally unpack them to see all the the goodies inside but for some reason nobody has made a program to re-pack them after they have been modified.
Now a nice thing to note is that you CAN still load partially unpacked files with the game and you can get around file size checks which means if someone makes a repacking tool then it might be possible to load modified stuff like AI and meshes and animations n stuff back into use. Why only half the tool exists... i dunno, it makes no sense to me.
All GBX would have to do is allow people to load unpacked folders...
