Its impossible. The games and saves use their own memory. Saves are stored in a readable and writable block of memory while the actual games are read only. Theres no way to replace the game with another. Game carts are mass produced, they aren't transferred one by one onto the actual chip set, this would take far to long. What they do is actually imprint the hardware with the game. So don't think of the memory where the game is stored as a hard drive but more of a chip that stores the game for read only operations.