19 It belongs only to an ecumenical council or to the Apostolic See to determine, transfer or suppress feast days common to all the Eastern Churches. On the other hand, to determine, transfer or suppress the feast days of any of the individual churches is within the competence not only of the Apostolic See but also of the patriarchal or archiepiscopal synod, due regard being had to the whole area and the other individual churches.
Source: Orientalium Ecclesiarum (Vatican.va)