It most likely would not change anything about the life of Jesus or how he is seen as some kind of "special" person. But it would change a lot on how religious people perceive virginity as something special. And no, "Behold a young woman shall conceive" is nothing special. And I somehow doubt that it was meant to be. Considering the value of women back in those days, I'd be very surprised if he wanted to draw much attention to Jesus' mother. It's actually a rather insignificant part of the prophecy, if anything, it's the lead-in rather than an important part of it. If you read the part (I guess we're referring to Isaiah 7:14 here, correct me if I'm wrong), you'll notice that the whole part about his birth seems more to have a temporal meaning rather than one of origin, that the future king is yet to be born and not already amongst them, rather than putting emphasis on him being born by that certain young woman|virgin. That's not the focus of the prophecy. It gets clearer if you read it in Hebrew, the meaning is rather one of a young woman who has not yet given birth. She may or may not be virgin, but the important bit is rather that this future king will be her firstborn, not so much the question whether she is virgin or not. The emphasis on the virginity is missing, the emphasis is on this future kind being her firstborn, something that was actually of high importance back then (compare for example the last plague of Egypt where all firstborn are killed, or Kain and Abel, where Kain is the firstborn and hence should be loved more than Abel, which leads ultimately to his jealousy, something that would by no means have been justified had he been the second born son).
But back to the change of effects this would have on the Church. It would not change the story much. Jesus would still be Jesus, no matter whether Mary is a virgin. What would maybe change, though, is our general moral situation and what we consider "moral" and "immoral". The emphasis on virginity would be much less. The same applies to other parts of the Bible where certain people, actions or omissions are allegedly "sinful", wrong or an offense to God. At any rate, I would not even remotely allow something like the King James version of the Bible be some kind of authority. Not even the Vulgata, not even the Septuaginta is beyond doubt. No matter what Pope or dogma says. Unless someone finds the original scripture, written by the original author who allegedly had some connection to God himself, doubt remains that errors were introduced by translation, or worse, deliberately added to further some agenda. Just think of the various Apocrypha written by "heretic" groups (especially common and popular amongst the Gnostics) where Peter, Thomas or even Judas allegedly wrote gospels that, surprise, surprise, further the Gnostic world view.
How can we be certain that something similar did not happen with the canon books somewhere in the millenia since their creation?