There's a problem when you reset the graphicsmode, using Graphics or Graphics3D: All loaded graphics and 3D stuff is erased. The handles are still there, but the media is gone, so it will MAV. What you can do is:
Pack all loading code into a reentrant function (one that can be called multiple times without to crash). Then right after the user altered the graphics mode, call the function to reload everything.
If you want the game to continue right where the player was before, then you need a powerful savegame/loadgame function, that I suggest to implement from the beginning on. It's hard to impossible to add a good savegame/loadgame functionality to an existing game.
Pack all loading code into a reentrant function (one that can be called multiple times without to crash). Then right after the user altered the graphics mode, call the function to reload everything.
If you want the game to continue right where the player was before, then you need a powerful savegame/loadgame function, that I suggest to implement from the beginning on. It's hard to impossible to add a good savegame/loadgame functionality to an existing game.