Candor est lucis aeterne...

..Et speculum sine macula.

I'm very happy that the Liturgia Horarum gives you the option to chose appropriate antiphons and hymns that may be different from those given, when there is no written melody or setting given for them in Gregorian chant. For the most part, I haven't taken this option. I think I've only done it on the feast of Our Lady of Mercy.
But I'm going to do it again very soon.
I'm using the antiphons from the old office 'Candor est lucis aeterne', the office for the feast of Our Lady of Lourdes before the Council. I am using the benedictus antiphon for Lauds, "praeclara salutis", but at I vespers I'm using the antiphon 'Ista est columba mea', and at II vespers, the antiphon 'Hodie gloriosa caeli regina' for the magnificat. Hymns, readings, and responsories from the common. Of course, the only problem is that I'll need nine antiphons for the office, but I'll only have five. For the other four, I can either repeat antiphons, or take some from the office of the immaculate conception.