If timetravel is to be considered then we must emphasize that when we say 'current preferences' we do not mean "preferences at time Time.now, whatever we can make those preferences be" but rather "I want things X, Y, Z to happen, regardless of the state of the atoms that make up me at this or any other time." Changing yourself to not want X, Y or Z will make X, Y and Z less likely to happen so you don't want to do that.