Actually if you want to get esoteric you can alter a lot of stuff in a dgen campaign including available player planes and how many AI planes of each type your side and the enemy have.
Some combo's simply never work for example you cannot fly a 109 over Singapore even if you manually edit the file with a 109 entry.
If you want to manually edit the DGEN files here is an older thread ....
http://forums.ubi.com/eve/forums/a/t...732#7131034732