Someone put to me this query: Suppose, in the future, it were to be decided by Authority that PF committed a formal act of Apostasy at the Vatican Gardens Event and thereby ceased to be pope. Would his act of canonising John Henry Newman still be valid?
Frankly, I regard this scenario as being in the very highest degree improbable. But ... what if ...
I would argue that, basically, it is what we Westerners nowadays call Beatification that really matters. (In the 'Orthodox' Churches, there has never been a two-stage ascent to Sainthood; just one stage.) In our Western Church, Beatification is the point at which the Church definitively permits a Catholic to be venerated by being given a Mass and Office in his honour; together with cultus. No longer are Masses to be offered for the repose of his soul. This change of status occurred when Pope Benedict beatified Newman at Birmingham. Canonisation simply extends the cultus from the restricted localities or communities specified in the decree of Beatification, to the Universal Church.
But even then things are not totally clear-cut. Not every newly canonised Saint is put on all the Universal Calendars as a memoria to be observed everywhere. (This is despite a hint in the writings of Pope Benedict XIV that a canonisation is not fully definitive unless acceptance of it is universally required.)
A little while ago, I accidentally came across a video made by Ann Widdecombe before Newman's Beatification. As a result of her enquiries and interviews, she expressed an opinion about why Benedict XVI was so keen for JHN to be beatified, and why, contrary to present practice, he wished to perform the rite himself rather than by delegation.
Absolutely correctly, Widdecombe focussed on the biglietto speech made by S John Henry upon receiving notification of his elevation to the Sacred College. In this, he asserted that throughout his life, both as an Anglican and as a Catholic, he had fought against what was for him the great error of the day: Liberalism. By this he meant what Benedict XVI called indifferentism and relativism: the idea that there is no absolute Truth.
Benedict beatified JHN by his own personal and direct act as a witness to the priority and certainty of the deposit of Faith handed down through the Apostles.
This theme has not been so much to the forefront of this pontificate ... before the canonisation, I did once make a jocular remark to the effect that people should pray that PF might not find out what Newman really stood for, before the scheduled date of the canonisation, lest the event be cancelled.
It is because S John Henry is not a witness to the predominant and abnormal themes of this present pontificate, but to an exactly opposite analysis, and because, unlike other modern canonizati, his elevation to the Altars of the Church is by the authority of two pontiffs, that I have confidence in the propriety of his cultus.
And, of course, God gave a very impresssive miracle as the witness to this great Saint's Sainthood.