I disagree with some posters above who have said no change to the mass could be heretical. Let’s start with the case in Australia where new Catholics were baptized in the name of the Creator, the Sanctifier, and the Redeemer. This is not strictly speaking heretical, as God is all of these things, and each person of the Trinity could be matched most closely with one of the labels. But it was questionable enough that the Church ruled it no longer constituted valid form, and therefore all those baptized during that period were invalidly baptized.
My point is that heretical statements and prayers could be introduced into the Order of the Mass in a similar way. One place where this was probably done was in a community in Canada where the belief was that God was not three persons, but five - the other two being the Blessed Virgin and some woman who I think was still alive and part of that group. If we look back at the history of the Church, we have recent knowledge of changes and experimentation that took place especially in the 1970s but in later decades as well. But we also have at least three other indications of great diversity in liturgy in the past:
*]Many local rites or uses were suppressed in favor of the Roman rite. Only those which could prove a certain age were exempted, and even fewer are still practiced today, such as the Ambrosian rite. Most major cities in Europe had their own rites, although these probably didn’t vary a great deal.
*]The long list of heresies is a list of Catholics who thought they were worshipping God correctly. For these heresies to come to prominence, they needed educated leaders to formulate and spread them. In most cases, this included priests. Some priests may have limited their heresies to the homily, but back in an era before the entire mass was as rigidly codified as it is today, it’s likely that some of these priests standardized certain heretical prayers or practices as part of the mass in that local Church.
*]If we look at the separated (mainly Orthodox) Churches whose origins date to the apostolic era, we can see a great diversity of practices and prayers that have survived. One has to assume that some changes veered into heresy, although most were reined in or corrected in time by contact with other Christians. Can we say that the 81 books of the Ethiopian canon are heresy-free?
So I think there are strong reasons to suppose that the mass has at times been changed to include heresy, but we have little direct evidence because such deviations have usually been suppressed.
