184 Hence, he would do something very wrong and dangerous who would dare to take on himself to reform all these exercises of piety and reduce them completely to the methods and norms of liturgical rites. However, it is necessary that the spirit of the sacred liturgy and its directives should exercise such a salutary influence on them that nothing improper be introduced nor anything unworthy of the dignity of the house of God or detrimental to the sacred functions or opposed to solid piety.
Source: Mediator Dei (Vatican.va)