Doctrine and dogma, for all practical purposes, are the same thing. They are all unchangeable.
Disciplines such as Lenten fasting and celibacy can change. They are not doctrines.
A lot of Catholic teaching falls into the category of theological opinion. This still holds a lot of weight because theological opinoin is derived from doctrine and doctrine is developed through theological opinion. While it is only an opinion, Catholics may disagree with it and the opinion can change. Once it is doctrine, Catholics may not disagree with it and it cannot change.
you fall to the confusion surroundin' the differentiation between doctrine and dogma. Now, what follows here is Church stance, so don't blame me for any of it - I figure its all superstition. Doctrine proceedes from dogma, and essentially is a matter of interpretation of dogma within the understandin' of the time. As such, doctrine is mutable, subject to formulation, change, revision, or rescision. Church doctrines are many, have come and gone, will come and go.
Dogma, on the other hand, is immutable; unchangin', unchangeable, unquestionable; it is, in the view of The Church, the direct and divinely revealed, incontravertible, uncontestable word of God. Dogma goes the the foundational core of Church teachin' - is in fact the theologic and moral core of The Church. There are in The Church far fewer dogmas than doctrines.
Doctrine is the work of Man in the name of The Church. Dogma, by Church definition, is The Word of God. Man is fallible, man changes. The Church recognizes and makes allowance for The Nature of Man. God and divinely revealed word are an entirely different matter - no allowance or accommodation may be made. Doctrine, though while in force must be obeyed, may be debated. Dogma must be accepted without question or reservation.