Can. 846 §1. In celebrating the sacraments the liturgical books approved by competent authority are to be observed faithfully; accordingly, no one is to add, omit, or alter anything in them on one’s own authority. GIRM 354. On Sundays, on the weekdays during Advent, Christmas Time, Lent, and Easter Time, on Feasts, and on Obligatory Memorials: a) If Mass is celebrated with the people, the Priest should follow the Calendar of the church where he is celebrating; b) If Mass is celebrated with the participation of one minister only, the Priest may choose either the Calendar of the church or his proper Calendar. GIRM 358. In the Lectionary for weekdays, readings are provided for each day of every week throughout the entire course of the year; hence, these readings will in general be used on the days to which they are assigned, unless there occurs a Solemnity, a Feast, or Memorial that has its own New Testament readings, that is to say, readings in which mention is made of the Saint being ce...