So then there is a litany written by the Church. Can it be added to at all? With legitimate, well-known, well-loved saints? For example, I don’t recall St. Polycarp being named in the Litany at the Vigil.
Yes, there are several versions of the Litany prescribed by the Church, including one for the Easter Vigil. In the rubrics for the Vigil, the Missale states, “In litaniis addi possunt aliqua nomina Sanctorum, praesertim vero Titularis ecclesiae vel Patronorum loci et eorum qui sunt baptizandi.” As I translate it, that means, “In litanies other names of Saints can be added, chiefly of the titular of the church or the patrons of the place and of those who are to be baptized.” Of course, it is the names of the
patrons of those who are to be baptized that can be added – we’re not adding the names of the baptizandi themselves as though
they were saints in the Litany.
This article should help, though please note that the Litany given at the end is not that for the Vigil. That list is as follows (I’m copying from the Latin, and there is an official English translation, but the saints are the same):
Sancta María, Mater Dei, ora pro nobis.
Sancte Míchael, ora pro nobis.
Sancti Angeli Dei, oráte pro nobis.
Sancte Ioánnes Baptísta, ora pro nobis.
Sancte Ioseph, ora pro nobis.
Sancti Petre et Paule, oráte pro nobis.
Sancte Andréa, ora pro nobis.
Sancte Ioánnes, ora pro nobis.
Sancta María Magdaléna, ora pro nobis.
Sancte Stéphane, ora pro nobis.
Sancte Ignáti Antiochéne, ora pro nobis.
Sancte Laurénti, ora pro nobis.
Sanctae Perpétua et Felícitas, oráte pro nobis.
Sancta Agnes, ora pro nobis.
Sancte Gregóri, ora pro nobis.
Sancte Augustíne, ora pro nobis.
Sancte Athanási, ora pro nobis.
Sancte Basíli, ora pro nobis.
Sancte Martíne, ora pro nobis.
Sancte Benedícte, ora pro nobis.
Sancti Francísce et Domínice, oráte pro nobis.
Sancte Francísce (Xavier), ora pro nobis.
Sancte Ioánnes María (Vianney), ora pro nobis.
Sancta Catharína (Senénsis), ora pro nobis.
Sancta Terésia a Iesu, ora pro nobis.
Omnes Sancti et Sanctae Dei, oráte pro nobis.