The rites of Canonisation have tended ... this will not surprise you ... to vary in the last seventy years. The most recent changes before this (PF) pontificate, which took place under Benedict XVI, seemed designed to impose on the rites a theological meaning which they previously had not so explicitly expressed. As Pope Benedict left the rite, before the singing of Veni Creator Spiritus the Pontiff asked for prayer that Christ the Lord would not permit His Church to err in so great a matter. And, in the Third Petition the Cardinal Prefect for the Causes of Saints informed the Pontiff that the Holy Spirit "in every time renders the supreme Magisterium immune from error (omni tempore supremum Magisterium erroris expertem reddit)".
These phrases, added by Pope Benedict, were in formulae cut out by PF when he canonised a number of beati in 2014; and subsequently.
It looks to me as though Pope Benedict's additions were intended to confirm the view that acts of canonisation are infallible and require acceptance de fide. I wish now to point out that, if the formulae introduced by Benedict XVI did affect this debated theological question, then, surely, so does the action of this Pontificate in removing them. In the gradual accumulation of evidences and precedents which gradually build up an established judgement of the Magisterium, surely phrases which were introduced into rites by one Pontiff and, very soon afterwards, removed by the next, have less auctoritas than established and immemorial formulae which have been used by successive pontiffs for centuries.
See also this blog entry at ccwatershed.