As Rorate Caeli was first to report in A.D. 1570, Pope St. Pius V promulgated Quo Primum, which established the Traditional Latin Mass for all time and decreed that no priest could be compelled to celebrate any other rite. Reading the entire thing is indeed salutary, but here again is the money line:
Furthermore, by these presents [this law], in virtue of Our Apostolic authority, We grant and concede in perpetuity that, for the chanting or reading of the Mass in any church whatsoever, this Missal is hereafter to be followed absolutely, without any scruple of conscience or fear of incurring any penalty, judgment, or censure, and may freely and lawfully be used. Nor are superiors, administrators, canons, chaplains, and other secular priests, or religious, of whatever title designated, obliged to celebrate the Mass otherwise than as enjoined by Us. We likewise declare and ordain that no one whosoever is forced or coerced to alter this Missal, and that this present document cannot be revoked or modified, but remain always valid and retain its full force notwithstanding the previous constitutions and decrees of the Holy See, as well as any general or special constitutions or edicts of provincial or synodal councils, and notwithstanding the practice and custom of the aforesaid churches, established by long and immemorial prescription – except, however, if more than two hundred years’ standing.
Thanks again to my brother, who reminded me of Rorate’s report and who is clearly on a roll today.