In the Office of Sundays, solemnities, … on ferial days of Lent and Holy Week … it is never permitted to change the texts which are proper or appropriated to the celebration. These include the antiphons, hymns, readings, responsories, concluding prayers, and, very often, the psalms. In place of the Sunday psalms of the current week, the Sunday psalms of another week may be substituted if desired. Especially in the Office with the people, other psalms may be chosen so as gradually to bring the people to a deeper understanding of the psalter.
I'm almost inclined to try and combine II Vespers with I Vespers, adding the psalms and canticle, and perhaps Magnificat antiphons to that office, which doesn't quite seem to contradict the GILH, since I'm not changing the proper texts, I'm just adding more of them to the same celebration
Saying both offices ... doesn't really violate any rules.
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