For some reasons I took several difficulty challenges before reading the notes and found them cannot be canceled.Finally I found a way to save my character saves.
Open the Player.chr with Hex Editor.Search for "all_n66" or "gamemodes" and then you'll see blocks represent for petless,hardcore,petonly or potionless.Delete skillLevel,skillEnabled,skillSublevel and skillActive(including the following dots).When you load your character again,the corresponding block will be deleted automatically and the buff will disappear.Hope it helpful for someone.