The Novus Ordo Missae of Paul VI is a schismatic invalid Rite, but lets suppose it was valid. Under no circuмstances should one attend it, because it is illicit.

Let me draw a parallel in which some might get what I am trying to say.

Case 1, you have a schismatic priest he is valid and uses a valid Catholic rite (all the eastern Rites they have kept really good), but he celebrates it against the Will of the Church. Thus he celebrates illicitly every time he consecrates the host. Theologians teach, most prominent among them the Angelic Doctor that sacraments from schismatics do not confer grace.

Case 2, A novus Ordo priest, celebrating the Novus Ordo Missae. So we are supposing for the sake of argument, a valid priesthood and a valid schismatic rite in the case of the Novus Ordo Missae. Now the new mass is similar to that of the Rite of the Nestorians, which was rejected by Rome for not having a narrative of the consecration. It is similar with respect to the fact that the rite is not considered Catholic, but made from scratch from schismatics (work of human hands and not the Holy Ghost). So that even if you have an undoubtedly Catholic priest who is celebrating that Rite, it would nevertheless despite the presumption that it would be valid is nevertheless incapable of conferring grace, because it is illicit to celebrate it. A more extreme example would be a Catholic priest celebrating the Satanic mass with the proper matter, form and intention (using a valid Satanic black mass), is another case of a schismatic Rite that cannot ever be celebrated licitly. I hope that I was able to get the point across, there are other examples. The New Mass is against the Will of the Church and because of that even if the priest innocently celebrates it not knowing any better, it would not change that fact it would only lessen his guilt (it would still be sinful). The only difference would be that the priest if he errs in good faith will not be guilty of the mortal sin of sacrilege, and blasphemy. A Catholic priest cannot celebrate the Nestorian Rite licitly, because it is a rite completely made from schism and it lacks the necessary criteria to make it 100% valid, since there is positive doubt that is sufficient to discard it. Rome has accepted the Rites of the Eastern Orthodox, and many of the Oriental ancient schismatic Churches is another story (some of them have been accepted, some of them not it just depends). If the Church accepts it, then it can be called a Catholic rite sometimes they just modify the Rite very little to make it properly Catholic.

+Pax vobis+