You are the one thinking legalistically. What you are missing is that the Catholic church is a body, a living organism headed by Christ who has designated in the apostles and their successors a means to resolve disputes, not to legislate in advance all the details. The Truth is Christ himself. We live in Christ, adhere to Christ, follow Christ, obey Christ, believe Christ. What exactly that means was relatively simple at the outset but has infinite room for deepened understanding because Christ is God incarnate and infinite. So as time goes on various people offered explanations of deeper understandings of who Christ was and of the structures (and therefore disciplines, rules and regulations) of his Body the Church. Some of the proffered explanations were ruled out of bounds, inadequate, erroneous, some were ruled in bounds by those appointed authorities (apostles, successors to apostles, with Peter's successor as the unifying final authority on earth).
So no, it never was and never will be and never can be laid out all nice and neatly in lists and decrees and rules because the Teaching is a Person, the Truth of the Universe, the Word of God Incarnate. He taught everything when he was here but his immediate disciples only understood a small fraction of it all--enough to be saved. He himself told them he would send his Holy Spirit to guide them into all truth and he appointed men to be the immediate tools of the Holy Spirit's guiding. Through this institution made by Christ himself, the unfolding of exactly what is reformable discipline and what is irreformable doctrine in ever increasing depth and detail takes place.
You have to trust the men Christ authorized to do the leading, themselves led by the Holy Spirit. Jesus did not think it wise to draft a written set of laws or a Constitution that would endure for all time. He put Himself as the living Constitution and Authority for his Body the Church but he from the beginning established his apostles as the means by which he through the Holy Spirit would govern this living organism.
So, some things (disciplines) changed, others developed without reversing or changing. The Catholic claim is that all this took place under Holy Spirit guidance. But you have to trust that. Your demand for a list shows a legalistic mindset and a failure to grasp the organic nature of the Mystical Body of Christ. It's very Enlightenment, Montesqueuian and non-Catholic. We have fallen back on written constitutions because we mistrusted the regiment of persons, princes etc. in the secular sphere. As we are now discovering, written Constitutions are worthless unless their caretakers are virtuous and intelligent and honest. We've failed at the task of taking care of our written US Constitution and will pay a terrible price for it (aborted babies being only one part of the price).
The Catholic claim is that written documents are secondary to the living organic authority of the persons Christ placed in charge and of their successors. It could only be trustworthy if indeed the Holy Spirit has been guiding it. These people Christ placed in charge do indeed use written documents to record their teaching, but that is actually only secondary to their doing the actual teaching. That's what counts--the actual teaching. Controversy always can arise and always will arise about the meaning of any written document. So a Catholic does not place his trust in the documents themselves or in any list of them but in the persons who taught the teachings recorded in them. And we'd be utter fools to place our trust in those persons if we did not first believe that Christ authorized these persons and has guided their successors through the Holy Spirit down through the centuries.
Therefore, if the current Holy Father (and before him John Paul II) are convinced that Limbo was never taught as an irreformable dogma (and on this every theologian of any repute would agree that they are correct), then instead of whining about them arbitrarily demoting a dogma to a discipline or an irreformable doctrine to a reformable one, we ought to accept their judgment that Limbo was never taught as dogma, but merely as theological speculation. If any body of historians or theologians were making a counter claim, insisting that Limbo was taught dogmatically, that would be one thing. But no one is making that claim who has any familiarity with the history of Limbo. The people who are throwing up their hands and accusing the Church authorities of arbitrarily abandoning settled doctrine are basing it on what the nuns taught them in school or on popular perceptions about what happens to the unbaptized infants etc.
The two doctrines that particularly concern me are both in the Catechism:
the wrongness of the death penalty,
and the limits on war (which John Paul II said the US failed to meet in Iraq).
Presumably, the Catechim's opposition to the death penalty and the Church's opposition to the war in Iraq as violative of the principles of just war, are neither of them infallible teachings?
The case for both doctrines seems pretty clear, and very ancient.
So, am I bound, as a Catholic, to oppose the death penalty and the war in Iraq? I believe that I am.
I do not oppose the war in Iraq. I think that the Pope was wrong, and that the just war doctrine, as stated in the catechism, is unworkable in the modern age. Times have changed, and what was good doctrine in an age of slow warfare actually is outright bad doctrine today, because it will lead to paralysis and, ultimately, more death if it's followed.
So, am I a disobedient Catholic because I oppose the Pope and the Vatican on the war in Iraq, and think that the Just War Doctrine itself, as specified, is unworkable, obsolete, and therefore simply WRONG in the modern age?
Is my disobedience sin?
Do I need to confess it and repent it?
I think that I am, in fact, an unrepentant sinner on this point.
I think that the doctrine is clear, ancient, and in the catechism.
I think that the Catholic Church has taken a clear position.
I think that position is bad, morally wrong, and if followed would lead to the horrible deaths of a lot more innocent people than the sharp, prophylactic war and democracy building that America is undertaken.
Nevertheless, I think that my view on this places me quite out of sync with the authorities of the Church.
I think that's clearly sin.
But I am not going to change my mind on it, because the Church is wrong and the US leadership was right on this.
So, do I CONFESS the sin, unrepentantly?
And if I die unrepentant, do I go to Hell for the sin of disobedience?
I take communion every week. Is this compounding my sin of disobedience? Is everyone Catholic in the pews who supports the war (or the death penalty) and thereby rejects the teaching on both by the Magesterium of the Church in a state of sin, to whom communion is denied until repentance?
Or doesn't this particular disobedience matter to God?
It's not an idle question.