Different game types / win modes

[fresbeeplayer]

Actually, I am partially working on this one. I needed a game mode for AI testing similar to "Practice" but not controlled by the user, and another without graphics (text mode only).
I found quite difficult modify the default game flow. I had to copy/paste a huge amount of code from game.cpp, because for example, I don't need a playing character, the main menu or the graphics at all.
Now I'm trying with declaring a separate class AI_TESTING friend of the class GAME, thus implementing new game modes invoking its methods.
I wonder if is possible to develop more general functions of the class GAME, like an API, so to avoid copying code that change from a rev to another?