To hack Crash files? Certainly some hacking can be done, but Crash levels are less amenable to that than most games. Everything is all chopped up into little chunks of data and packed together very tightly so you can only modify content in place and not increase the size of something. There is also a lot of precomputing in crash so the content interlocks together. If you changed the background, the visibility and collision data needs to be recomputed. This would be nearly impossible to do to the final data. We did it by modifying the big original in Alias and then recomputing the level. This process took several hours split across 5 SGI workstations.