This is about how to celebrate memorials in Advent. I have consulted Fr Aurelio, Fr Stephen, and also the General Instruction on the Liturgy of the Hours. Fr Aurelio writes:
"1. Until the 16th of December, they can be observed as normally throughout the year. (see Gen. Instr. on the Lit. of the Hours, n. 235).
- In the Liturgy of the Hours, this can range between a minimum observance(taking only what is Proper from the memorial: Concluding Prayer; the occasional Bened./Magn. Antiphon) and a maximum observance (taking also the Hymn and Short Reading onwards from the Common of the Saint). (GILH n. 235)
- Personally, I would generally go for a minimum observance of the memorial, so as to maintain as many Advent elements as possible. Thus, for example, on the 13th of December, the Preface at Mass can either be that of Advent I (my preference) or that of Martyrs.
2. From the 17th to the 24th of December: Any memorials can only be treated a Commemorations. (see Gen. Instr. on the Lit. of the Hours, n. 238)
- In the General Calendar there is Peter Canisius (21st) and St. John of Kenty (23rd).
- During Mass, the only thing that can be done (as an optional) is to use their Collect. Nothing else.
- During the Liturgy of the Hours, their concluding prayer (and Antiphon, if their is one) could be added at the end. (GILH n. 239)."
So: there an option between the minimum and the maximum observance all through the year, and also in Advent till 16 Dec.
Practically: I recommend the minimum observance so as to respect the proper of Advent.