There are many aspects of Catholic teaching that can be modified and refined, as well as rules of discipline, but the doctrinal moral and theological teachings

There are many aspects of Catholic teaching that can be modified and refined, as well as rules of discipline, but the doctrinal moral and theological teachings of the Church cannot be changed. For instance, "No meat on Fridays during Lent" is a rule of discipline and bishops are free to modify this or even eliminate it should they wish. Holy Days of Obligation, aside from every Sunday, are also disciplinary rules, and are sometimes different from diocese to diocese, even within a single country (like the U.S.). Priestly celibacy is also a discipline rule that could be modified (but almost certainly won't be, IMO). It's only been universal in the Roman Church for about 1000 years or so, and some Rites allow for married priests, which is fine. But the immorality of murder, abortion, sex outside of marriage, the definition of marriage, etc., etc., as well as teachings regarding the Divinity of Christ, the Real Presence and the Sacraments, are moral and theological doctrines of the Church and not subject to revision, and any Pope or bishop that attempted to claim otherwise would be engaging in material heresy. Now having said that, discipline with respect to the correct teaching of Catholic doctrine has massively broken down (e.g., the monks you described) in the past half century, but that doesn't make it right, and it will eventually be corrected. At one point the vast majority of the Church was Arian, but that wasn't right either, and was eventually corrected as well. The Church was established by Christ, and exists to correctly pass down His teachings. It is only serving its members by passing down those teachings, which are not subject to change, and by properly exercising the authority granted to it by Christ. Church Doctrine has never changed, and cannot and will not change. This is why there are over 40,000 Christian denominations which split off from the Catholic Church and from each other by attempting to change doctrine.