I take the points that others have made, namely that the priest in question is a foreigner, and that the Mass was valid as long as he said the essential words “This is my Body…This is my Blood”. However, I would make the following observations. **Firstly, a foreign priest is still presumably reading from the Roman Missal, in which case it is strange that he would add the word “remission” or improvise a preface or post-Communion prayer. In fact, surely it would be more difficult as a foreigner to ad lib rather than merely follow what the Church has approved in the Roman Missal. I’m not saying that you should come down heavy-handed with this priest, but I don’t see how one can “accidentally” improvise a preface if one is reading from the missal. **Sacrosanctum Concilium, for example, is very clear that “…no other person, even if he be a priest, may add, remove, or change anything in the liturgy on his own authority” (SC22). In addition, the more recent document, Redemptionis Sacramentum states:
“The reprobated practice by which Priests, Deacons or the faithful here and there alter or vary at will the texts of the Sacred Liturgy that they are charged to pronounce, must cease. For in doing thus, they render the celebration of the Sacred Liturgy unstable, and not infrequently distort the authentic meaning of the Liturgy” (RS59).
While the Mass was indeed valid, I think we should be concerned that Catholics feel they have to ask whether a certain Mass was valid or not when the liturgy is rendered unstable by priests altering parts at will.