A strict discipline (i.e. law) is not a matter of faith and morals, i.e. the communion fast, or rules for excommunication, or rules for when feast days are celebrated. These are human laws, which St Peter has the power to 'bind and loose'. Divine Law and Divine Truth cannot change and infallibility's purpose is to guard and protect that which is unchangeable, which no pope can change. Again, a lack of distinctions is your problem.