Is Humanae Vitae reformable? How???

Granting of course that Humanae Vitae is not infallible.

Just for the sake of argument, let us assume that the teaching which says "contraceptives are intrinsically wrong" is reformable, meaning that the infallibility accorded to the ordinary and universal magesterium, when it teaches consistently in a definitive and authoritative manner - does not apply in the case of this core teaching of Humanae Vitae. Let us look at a hypothetical instance wherein the Church actually decides to make a complete turn-around and has to repudiate Humanae Vitae, in order for the Church to be "relevant to the times" and "responsive to its flock".

1. First of all, it has to infallibly reinterpret Vatican II's declaration on the ordinary and universal magesterium's infallibility (Lumen Gentium # 25). It has to reverse or drastically reinterpret the repeated affirmations of Pope John Paul II, the affirmation of Pope Benedict XVI, and the declaration of Pope Pius XII. I see at least five papal encyclicals it has to reverse, drastically reinterpret, or throw out altogether: Castii Conubii, Humanae Vitae, Evangelium Vitae, Familiaris Consortio, and Veritatis Splendor. On top of that, we still have to consider what the Early Church Fathers and the Patriarches had to say in the intervening years. All the reversals must be pronounced ex-cathedra, or else the argument will just run around in circles. That requires a mighty bit of undoing, and would presumably be the first ever time the Catholic Church will take a stand of demonstrating the right to be essentially wrong and to reverse itself if need be. Anglicans would make for good company here.

2. Forty years since Humanae Vitae (HV) is a long time. The Church must prove that the lessons of the past 40 years only serves to disprove HV, necessitating its reversal. The empirical equation must now take into consideration Pope Paul VI's four dire predictions, and whether they were proven true or not. It will now be tasked to investigate statistical data on teenage pregnancies, unwed mothers, marital abuse, abortions, promiscuity, venereal diseases, coercive legislations, forced sterilizations/ abortions, broken families, eugenics...and offer to prove empirically and infallibly that in our experience over the last 40 years, Pope Paul VI's predictions are nothing but thin air.

3. This move will actually boil down to essentially adopting the Anglican Church's position in the Lambeth Conference of 1930, which states: "Where there is a clearly felt moral obligation to limit or avoid parenthood, complete abstinence is the primary and obvious method, but if there is morally sound reasoning for avoiding abstinence, the Conference agrees that other methods may be used, provided that this is done in the light of Christian principles.". With this retroactive stand, the Church will retire the "intrinsic evil" in contraception, but it has a lot of explaining to do why in the first place it disagreed with the Anglicans 78 years ago, only to take the same, same position today.

4. The Church will also have to address the issue of the so-called "demographic winter", an irreversible demographic crisis arising from low birth-replacement rates, a natural consequence of a high penetration of artificial contraceptives combined with an averse attitude to child-bearing. To justify a reversal, the Church must offer a workable solution here, something the European countries, Japan, and Singapore are still at a loss on how to solve.

5. Again, is Humanae Vitae reformable? Has the Ordinary and Universal Magesterium displayed enough ambiguity for ample wiggle room? Are there other workable ways around it?
It is said that there are many ways you can skin a cat. But not when you're down to the bones.