Hacking the ROM will have very little to do with your ability to turn it into an MMO. The one thing it'll help with is general familiarity with the ROM (where things are, what pointers are, some assembly, etc) but the actual programming is pretty tricky.
I was messing around with a single player version back in the eternal days (RIP in pieces) but it was a lot more work than I expected, so I dropped that shit.
So no - not easy, unless you're a brilliant developer familiar with asynchronous development, ROM parsing, rendering, etc, etc...