Well I think it would mean quite a lot would have to change. Your religion teaches that ex-cathedra proclaimations are inerrant. The dogma that states the perpetual virginity of Mary was also claimed to pronounce "anathema" on anyone who did not believe it, as I understand it. The Perpetual Virginity of Mary is a doctrine of De fide (of the faith). It is a "theological note" or "theological qualification" that indicates that some religious doctrine is an essential part of Catholic faith and that denial of it is heresy. So, yes, it would actually mean that the "Church" was actually wrong about something and would blow that whole "inerrancy" bubble sky high.
We know that many "traditions" from the past can be based on myths or legends so not all traditions are necessarily true. That is why God gave us scripture as our rule of faith. People don't always get things right. God is never wrong.
And that, dear lady, is also a myth. Blind belief in the Bible's inerrancy is no different than any other blind belief. You make a brilliant critique of the de fide acceptance, and then turn around and express the same de fide acceptance yourself.
Of course it would, you are correct. I took the question to mean: what other dogmas are built on this one, and none is, but of course the perpetual virginity itself is a doctrine that is to be believed by all who desire salvation. I am sorry if it seemed otherwise. It is not an optional belief.