CathInfo.com

Infallibility has to do with faith/morals.  It does not have to do with discipline.  If you disagree, give me an example.

46. On this subject We judge it Our duty to rectify an attitude with which you are doubtless familiar, Venerable Brethren. We refer to the error and fallacious reasoning of those who have claimed that the sacred liturgy is a kind of proving ground for the truths to be held of faith, meaning by this that the Church is obliged to declare such a doctrine sound when it is found to have produced fruits of piety and sanctity through the sacred rites of the liturgy, and to reject it otherwise. Hence the epigram, “Lex orandi, lex credendi” — the law for prayer is the law for faith.

47. But this is not what the Church teaches and enjoins. The worship she offers to God, all good and great, is a continuous profession of Catholic faith and a continuous exercise of hope and charity, as Augustine puts it tersely. “God is to be worshipped,” he says, “by faith, hope and charity.”[44] In the sacred liturgy we profess the Catholic faith explicitly and openly, not only by the celebration of the mysteries, and by offering the holy sacrifice and administering the sacraments, but also by saying or singing the credo or Symbol of the faith — it is indeed the sign and badge, as it were, of the Christian — along with other texts, and likewise by the reading of holy scripture, written under the inspiration of the Holy Ghost. The entire liturgy, therefore, has the Catholic faith for its content, inasmuch as it bears public witness to the faith of the Church.

Upon confirmation by the Pope, a General Council's decrees are binding on all Catholics.

It is true that discipline is man-made and can be changed. However, and this is very important, the Authority to enact discipline is not man-made, but given by God.

Pope Gregory XVI, Quo graviora of 1833:

Mediator Dei, Pope Pius XII, 1947

  Pax declares Papal Teaching that the Church cannot permit anything to the detriment of souls "Irrelevant".