The Game Genie code EEOGAAAA enables a small debug mode. On the title screen, you can press Left or Right for a level select (though be aware that the controls are backwards. Left goes up one level, and right goes down one level).
In-game, pressing Start + Select resets the game and brings you back to the title screen. While paused, pressing "A" and "B" changes the gamma coloration of the maze.