Well, I wish I could help, but I'm not a coder, and I don't think anyone on here has C++ knowledge...just lua scripting, and hex editing.
And FYI, that's just the PS2 version. The rest run on GameBryo, which is the same engine as the one for ESIV: Oblivion, and Fallout 3.
But whether a game is mod-able has nothing to do with the engine...it depends on how the developer coded the game.