The Catholic Church may change that which is* ecclastical* law not divine law. From The Pontifical Council for Promoting Christian Unity (Vatican source):The Catholic Church considers the words of the Institution as a constitutive part of the Anaphora or Eucharistic Prayer. The Council of Florence stated “
The form of this sacrament are the words of the Saviour with which he effected this sacrament. A priest speaking in the person of Christ effects this sacrament. For, in virtue of those words, the substance of bread is changed into the body of Christ and the substance of wine into his blood” (D.H. 1321). The same Council of Florence also characterised the words of the Institution as *“the form of words [forma verborum] which the holy Roman Church …] has always been wont to use [semper uti consuevit] in the consecration of the Lord’s body and blood” *(D.H. 1352), without prejudice to the possibility of some variation in their articulation by the Church. **Although not having any authority as to the substance of the sacraments, the Church does have the power to determine their concrete shaping, regarding both their sacramental sign (materia) and their words of administration (forma) (cf. CCEO, can. 669). ** Hence the doctrinal question about the validity of the Anaphora of Addai and Mari, when used in its short version without a coherent Institution Narrative. Do the words of administration (forma) correspond to the conditions for validity, as requested by the Catholic Church? To answer this question, three major arguments have to be taken into due consideration.
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So the words of the Institution are not absent in the Anaphora of Addai and Mari, but explicitly mentioned in a dispersed way, from the beginning to the end, in the most important passages of the Anaphora. It is also clear that the passages cited above express the full conviction of commemorating the Lord’s paschal mystery, in the strong sense of making it present; that is, the intention to carry out in practice precisely what Christ established by his words and actions in instituting the Eucharist.
A long and careful study was undertaken of the Anaphora of Addai and Mari, from a theological, liturgical and historical perspective, at the end of which the Congregation for the Doctrine of Faith on January 17th, 2001 concluded that this Anaphora can be considered valid. Pope John Paul II subsequently approved this decision.
vatican.va/roman_curia/pontifical_councils/chrstuni/documents/rc_pc_chrstuni_doc_20011025_chiesa-caldea-assira_en.html