Yes. If anyone still doubts the validity of the new rite after Pope Benedict XVI was manifestly universally accepted (and therefore known to have become Bishop of Rome) in Rome, he ipso facto commits an objective mortal sin and denies two dogmatic facts (1) that Pope Benedict XVI, in 2005, was Sovereign Pontiff of the Universal Church. (2) that Pope Benedict XVI, in 2005, was the reigning Bishop of Rome, and therefore known with infallible certainty to be a valid Bishop. In other words, just as the fact alone of Universal Acceptance proves infallibly the existence of all the conditions required, and makes continued doubt regarding his person as Pope sinful and illicit, it also makes continued doubt of the validity of the rite in which he was consecrated Bishop likewise sinful and illicit. In 2007, there was an excellent study by Fr. Pierre Marie, proving from two Eastern rites, the Coptic and the West Syrian, that the NREC is surely valid.
Some of the careless people here don't say that they make an absolute mockery of the Roman Catholic religion by professing and teaching as their own self-invented dogmatic fact that rites the Roman Church has used for 50+years are invalid. Get ready to see mor people running to the Eastern Orthodox Churches, then, as we've already seen, as you yourself undermine the Roman Church so badly.