108. One and the same Priest must always exercise the presidential function in all of its parts, except for those parts which are proper to a Mass at which the Bishop is present (cf. above no. 92).
Y’all knew about this one with priests, right? There’s a fairly common practice for one priest or deacon to preach all the Masses–my parish used to do that under its former pastor. However, practical for homily prep, that would seem to be out of kilter with what the GIRM is driving at here.
109. If there are several present who are able to exercise the same ministry, nothing forbids their distributing among themselves and performing different parts of the same ministry or duty. For example, one Deacon may be assigned to execute the sung parts, another to serve at the altar; if there are several readings, it is well to distribute them among a number of readers, and the same applies for other matters. However, it is not at all appropriate that several persons divide a single element of the celebration among themselves, e.g., that the same reading be proclaimed by two readers, one after the other, with the exception of the Passion of the Lord.
I can think of only one or two possible pragmatic exceptions, perhaps when the prayers of the faithful might be rendered partly in song.
110. If at a Mass with the people only one minister is present, that minister may exercise several different functions.
But in this instance, the Mass would probably be very lightly attended.
One final pep talk:
111. There should be harmony and diligence among all those involved in the effective preparation of each liturgical celebration in accordance with the Missal and other liturgical books, both as regards the rites and as regards the pastoral and musical aspects. This should take place under the direction of the rector of the church and after consultation with the faithful in things that directly pertain to them. However, the Priest who presides at the celebration always retains the right of arranging those things that pertain to him.[Sacrosanctum Concilium 22]