Many of the “new things” that crept in over time were codified at Trent. As a result of the implementation of Trent, several very ancient liturgies were abolished. The Mass of Trent was also imposed on communities that never used it – it was quite new for them.
Pope Pius V himself changed the Missal and added the feast of Our Lady of Victory
His immediate successor, Pope Gregory XIII, changed the name of this feast to “The Most Holy Rosary of the Blessed Virgin Mary”
Pius V’s work in severely reducing the number of feasts in the Roman Calendar (see this comparison) was very soon further undone by his successors. Feasts that he had abolished, such as those of the Presentation of Mary, Saint Anne and Saint Anthony of Padua, were restored even before Clement VIII’s 1604 typical edition of the Missal was issued.
While keeping on 8 December what he called the feast of “the Conception of Blessed Mary” (omitting the word “Immaculate”), Pius V suppressed the existing special Mass for the feast, directing that the Mass for the Nativity of Mary (with the word “Nativity” replaced by “Conception”) be used instead. Part of that earlier Mass was revived in the Mass that Pope Pius IX ordered to be used on the feast.
In the 300 years after Trent (before Vatican II), many “new things” had crept into the Mass also
Protestant music: Bach, Hassler, Tallis
Vernacular hymns
Translations of the Mass texts into English
The use of handmissals
Dialogue Mass
A completely new Holy Week ceremony
A comparison between Pope Pius V’s Tridentine Calendar and the General Roman Calendar of 1954 shows the changes made from 1570 to 1954. Pope Pius XII made a general revision in 1955, and Pope John XXIII made further general revisions in 1960 simplifying the terminology concerning the ranking of liturgical celebrations.
After Pius V’s original Tridentine Roman Missal, the first new typical edition was promulgated in 1604 by Pope Clement VIII, who in 1592 had issued a revised edition of the Vulgate. The Bible texts in the Missal of Pope Pius V did not correspond exactly to the new Vulgate, and so Clement edited and revised Pope Pius V’s Missal, making alterations both in the scriptural texts and in other matters. He abolished some prayers that the 1570 Missal obliged the priest to say on entering the church; shortened the two prayers to be said after the Confiteor; directed that the words “Haec quotiescumque feceritis, in meam memoriam facietis” should not be said while displaying the chalice to the people after the consecration, but before doing so; inserted directions at several points of the Canon that the priest was to pronounce the words inaudibly; suppressed the rule that, at High Mass, the priest, even if not a bishop, was to give the final blessing with three signs of the cross; and rewrote the rubrics, introducing, for instance, the ringing of a small bell.
In 1911, with the bull Divino Afflatu,[36] Pope Pius X made significant changes in the rubrics. He died in 1914, so it fell to his successor Pope Benedict XV to issue a new typical edition incorporating his changes. This 1920 edition also included a new section headed: “Additions and Changes in the Rubrics of the Missal in accordance with the Bull Divino afflatu and the Subsequent Decrees of the Sacred Congregation of Rites”. This additional section was almost as long as the previous section on the “General Rubrics of the Missal”, which continued to be printed unchanged.
en.wikipedia.org/wiki/Tridentine_Mass
