I do not think it is even allowed for anyone to create a new missal, even it it rots on a book shelf.
Well, if QP doesn't prohibit it, then it's allowed, by default.
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But either way, the NO missal is not entirely new in the sense you are talking about because some parts of the NO missal retained certain parts of the Roman Missal, which means the Roman Missal was revised or altered into the NO missal - which makes the NO missal illegal:
I agree that the NO is not 100% new, but that's beside the point. Paul 6 issued a new missal, regardless of if the contents of the missal are 100% new. Legally, Paul 6's missal is not a revision, but an entirely new missal. Yes, whether it's a revision or new, it's still illegal (to use) regardless.
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"We likewise declare and ordain that no one whosoever is forced or coerced to alter this Missal, and that this present docuмent cannot be revoked or modified....Wherefore, in order that the Missal be preserved incorrupt throughout the whole world and kept free of flaws and errors, the penalty for nonobservance for printers, whether mediately or immediately subject to Our dominion, and that of the Holy Roman Church...."
I believe this passage is why the Modernists chose to call Paul 6's missal the "new order". They did not want it to be confused with a revision of the True Mass. In my opinion, God would not allow this level of confusion/deceit, so the Modernists had to be content with the legal definition of "new". They knew they could not abrogate/delete the True Mass; the only way to get rid of it is to create a false liturgy that people would "prefer" and so get rid of the True Mass indirectly.