Two things: please, segment this off into legible sections, please. Separate the plot, the gameplay, and the characters.
Second thing, as to your last question, you probably could modify the games that much, but the fact remains that this is the Game Development section, not the Romhacking section. You do not modify games here. You create them from scratch.
As an extra note, please, grammar and spelling are your friends. Bring them to the table. It'd make it a lot easier for me and anyone else to comment on this.