With many video games, there's no "game over" screen, no reason to ever get bored. In a long-standing practice called "modding," fans create their own new chapters, artwork and other twists to extend the lives of their favorite games. Many game makers freely encourage the practice and give away free software tools to help. But some in the industry are now wondering about the ratings implications posed by mods after a Dutch programmer created one that unlocks a hidden sex level in the violent action game "Grand Theft Auto: San Andreas." After all, video games aren't like the feature films...