may i have to put this there...
if you look in youtube and others sonic pages, there are some sweet mods for sonic generations such as
CSA (or classic in modern and modern in classic)
Fixing sonic forever
Super sonic generations
and upcoming ones: blaze generations, silver generations (with flying), sonic melpontrerations, sonic adventure generations (this one is a candy for the eye), sonic unleashed generations (with classic sonic as night stages) and so much more coming!
but well... they are for pc version, and i'm sure that you realized thet the pc version is near the same as xbox360 version, plus with some files that are for the pc adjust and controls.
the bb, bb2 and bb3.cpk (where everything is inside) files are nearly the same, and the files that the hacks uses are present in both versions
i still dont have jtag xbox360, so i can't try this (i tried but then my xbox360 didn't recognize my disc), but if somebody can try this
here is a video proof of concept
this tool helps by installing and mixing mods
this is for extract, but there is another program that is a cpk packer/unpacker but i cant find it know... sorry.,