Maybe the best is made a totally new American Football (and also other sports games). I don?t know but maybe the work to change an existent game to insert adversaries A.I could be the same or more?
Agreed, changing it's much more trouble. Disassembling a ROM and understanding it takes a considerable amount of effort. Also, oldschool assembly code like that is not really position independent, so good luck reordering everything and keeping track of state.