The classic definition of heresy is the refusal to believe truth. Since the Pope insists that what he says is truth and he back it up in Evangelium Vitae, then you are in a conflict with his authority.
The Holy Father said in Evangelium Vitae that the Church has moved away from the former position regarding the death penalty, but he also adds that he has the authority to allow that move and that he is allowing it and promoting it. The argument would have to be found that says that he does not have the authority to allow the Church to move away from its former position. [Precisely, but you haven’t heard it yet.]
It is the Prefect’s role to point out any doctrinal or moral errors in such a document.
My friendly suggestion is that Catholics accept a) that the pope has the authority to revize moral law without changing truth, b) that he has the authority to review previous moral teachings and say that their application (not the subject) can change and has changed, and c) that the pope has authoritatively changed the rules and made them more stringent. He has not come out and said that the death penalty can never be used. He has said that the circumstances that would require it are very rare, if they exist at all. He’s leaving that margin for the possibility that there is a need to use it.
The problem is that these teachings were laws, not doctrines. Laws can and do change. These laws were based on what was known at the time and what was reasonable at the time.
I have noticed elsewhere that you have several advanced degrees in theology - so how could you so completely elide the hierarchy of truths and their relation to the charge of heresy? Heresy is the pertinacious doubt or denial of a truth whose acceptance the Church requires
de fide. The ordinary papal magisterium, on the other hand, does not require this level of assent, only the religious submission of mind and will. You will note that the point in
EV where John Paul invokes his Petrine authority is, at any rate, in relation to the teaching on abortion, at which point he also does
not invoke an extraordinary authority to bind on the matter, instead noting that as Peter he is pointing out the constant teaching of the universal magisterium (much as he did on the matter of an all-male priesthood, where both he and his cardinal prefect of the CDF - whom you have mentioned - unequivocally affirmed that no extraordinary magisterium had been exercised). But if we are in the realm of the ordinary magisterium, we must, as has already been said, read John Paul’s teaching in continuity with the previous magisterium.
You also continue to have a highly circumstantial notion of the moral law. The moral law itself is unchanging, although portions of it require specification through positive law. For example, one is bound to “honor the Sabbath day,” which the Church specifies as assisting at a Catholic Eucharistic liturgy any time from Saturday evening to Sunday at 11:59 pm. One could equivocally say that an ecclesiastical modification of this Sunday obligation would amount to “changing the moral law,” but what is really happening is that through positive legislation he is bringing otherwise indifferent acts into new relation to the unchanging moral law. As a teacher the pope, he expounds the eternal, as a legislator he attaches the temporal to it. He issued no positive law on the matter of capital punishment.
So it is patently false to say that “moral teachings are binding until they are loosed by a pope.” Moral teachings are true or false; true teachings can leave room for prudential application, but they cannot be overturned by a future pope. The magisterial loci cited by the critics of John Paul’s teaching on capital punishment are most certainly not
ad hoc laws - they are general and unqualified statements about the justifications for the death penalty. Each one individually is also but one piece of the ordinary magisterium, but collectively they form a univocal whole throughout the history of the Church - something known as the universal magisterium, the same magisterium on the basis of which we can condemn abortion, contraception, and women’s ordination. It was on this basis that Cdl. Dulles and others well-acquainted with the tradition asserted the John Paul’s teaching must be a prudential judgment of how best to apply the truths about the death penalty (with its uncontested four ends) to present circumstances. Cdl. Ratzinger could have performed his duty just fine by adopting the same understanding.
Now we could also step back from the issue to look at it another way. You yourself keep asserting that John Paul’s teaching was meant to change the truth to fit new modern circumstances, in which case we can be assured that he did not mean to assert anything about the unchanging moral law, and thus did not mean to universally bind Catholics to a teaching. Furthermore, if his teaching is based on circumstances, Catholics would not be bound to follow him, because the pope does not have a magisterium that extends to the factual conditions of prison systems. The pope could never infallibly proclaim that St. Joseph County Jail has sufficient security measures to ensure that its prisoners harm neither the general or prison populations. Even if my shirt is in fact green, the papal magisterium does not have the authority to bind Catholics to believe it - it is not a matter of faith or morals. So if the pope cannot authoritatively establish matters of physical fact in that matter, he cannot authoritatively establish the existence of the conditions upon which you propose his alteration of Catholic truth was premised. You’re working from an inflated notion of the papacy.