Well, many can also mean all men. St. Paul, after all, says:
For just as through the disobedience of the one man the many were made sinners, so also through the obedience of the one man the many will be made righteous.
In which he surely means the same as he says in that same chapter of the epistle: "sin entered the world through one man, and death through sin, and in this way death came to all men, because all sinned".
And since this seems so, it doesn't seem impossible that the words should mean two different things at the same time, just as "the rock" means both St. Peter and his confession of faith.
Secondly, the Church has already spoken on the subject:
The Catechism is referring to the traditional rite. It is obvious to all that it is permitted to the Church to modify the words of consecration, so long as the form expresses the grace which the Sacrament effects and signifies: the variety of different rites makes this clear, especially the addition of the "mysterium fidei" to the Roman liturgy.
So I don't see any impediment to understanding that Rome has added the sufficiency of Christ's Passion as at least a secondary understanding of the words "pro multis" in the reformed rite, which can be proved from the Roman approval of the translation "for all".
I'm boggled by the defense of this lie. According to Sacred Scripture, Christ said "for many". It doesn't matter what you, or any other armchair theologian thinks He meant. IT'S WHAT HE SAID THAT MATTERS. Not you or the Pope can change what He said and to misquote Him is a lie.