Does the New Mass Violate Trent’s Decree?

The canon to which you refer only limits the clergy from changing the rites of their own accord. The Church still does not permit priests or bishops to change the approved liturgies of the Church at their whim (Code of Canon Law, can. 214; Constitution on the Sacred Liturgy, 22.3).

The Council of Trent recognized the right of the Church to make changes to the rites of the Church:

It declares furthermore, that in the dispensation of the sacraments, the Church may, according to circumstances, times and places, determine or change whatever she may judge most expedient for the benefit of those receiving them or for the veneration of the sacraments; and this power has always been hers (Council of Trent, session 21, chapter 2).