As announced earlier, today the USCCB Secretariat of Divine Worship released the resource Liturgical Notes and Resource Materials for use Upon the Resignation of the Pope, for use in the weeks that lie ahead. The full release can be found here.
Among other things, it recommends the use of a Mass for Various Needs:
The Roman Missal provides a Mass formulary for a Pope. It can be found in the section, “Masses and Prayers for Various Needs and Occasions: 2. For the Pope.” This Mass is permitted, with white vestments, on weekdays in Lent “at the direction of the Diocesan Bishop or with his permission” (General Instruction of the Roman Missal [GIRM], no. 374), but not on the Sundays of Lent.
There are no musical settings for the antiphons given in this Mass. For those who would like to sing these antiphons in simple English chant, please consider the following musical settings (free download):