353. On Solemnities the Priest is obliged to follow the Calendar of the church where he is celebrating.
An obvious case of the priest bowing to the pastoral and spiritual need of the laity–not to mention the practice of the universal Church.
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;
See comment above.
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.
If the priest is on his own, he may choose the calendar of his religious order or diocese.