I plan on using Attende Domine; although, I also have the little booklet from the Papal Ash Wednesday Mass so I will see what they did and try to match it. I believe that they used the Attende Domine for the Offertory.
One option could be O Sun of Justice or Our Father, We Have Wandered.
Immutemur habitu by Fr. José Maurício Nunes García (1767–1830) [PDF]
This will be the second year we will sing this work; we will sing Psalm 50(51) in its entirety in a harmonized Mode II psalm tone between repetitions of this piece. The choir has taken a real appreciation to this piece and its example of the universality of the Church's treasury of sacred music. (Brazilian Baroque? Yes!)
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