Interesting stuff, do you have any idea exactly how Gunheds rank system works? I haven't looked into it specifically but I think it just works off of your power up level. An easy setting for low power, a normal setting for in the middle and a hard setting for high power. The high power area seems to only kick in with certain maxed out weapon combos afaik. I've only really noticed it on the second level boss, most of the time he only shoots 1 triangle tracking-missile but with certain maxed out weapons like a II and F combo he will shoot two triangle missiles. I assume other stuff gets ramped up too, but not sure.
I wonder if it works like this.. non selectable Easy, Normal Dog(default), Hard Human, Super Mania, God of Game, non selectable Hardest and it just switches 1 up or 1 down depending on your power up level. If this is the case, it could mean we could hack in the two extra modes.
I could be entirely wrong..