Enable the "Change health level", "Change magicka level", or "Change fatigue level" codes, and before you fill your health/magicka/fatigue up, while holding A and filling it, press B and exit. It will continue to rise and as it goes down, it will raise back up instantly. For example, start filling your health/magicka/fatigue, and press B before it is to the top, While still holding A and filling it, it will keep and always be full until you return to the menu.