This request could certainly be answered by individuals or small groups, such as prayer groups. However, it is even more appropriate if the People of God are united in fulfilling this request. The one time when this can be done is when “everyone” is gathered for the Sacred Liturgy.
In light of the liturgical norms, it becomes problematic, however, if the whole assembly, led by the celebrant, prays it in apparent continuation of the liturgical action just completed. Once the celebrant processes out, though, the Mass is clearly ended. It is no more contradictory for the assembly to join in the Prayer to St. Michael, then it is to break up and depart, as either action is now distinct from the Mass. In the same way, the rosary said immediately before Mass by the faithful, but not incorporated into its beginning, does not contravene the distinction between liturgy and devotion.