Well, I don't thin it would change Judaism that much- a few other prominent Jews claimed to be and were accepted as the messiah. For Jesus to be accepted, well for one, he has to not die shortly after entering Jerusalem and be crucified.
The end result: Jesus ends up like any other powerful "messiah" accepted by the Jews under Roman occupation-he leads an initially successful rebellion, the rebellion gets crushed when the Romans return shortly thereafter, Jesus is killed, and Judaism returns to Judaism.
No, just no. A small minority, a very small minority (at least until Paul) did. That minority was shunned mostly by the Jews in Palestine. It was only when they branched out to the "Hellenized" Jews living in other areas of the empire, that they had any success getting converts.
Even then, the majority of converts to Christianity were not Jews.
edit: Also, I should point out that until the failure of the Great Jewish Revolt of 66-70, mainstream Christianity remained a sect of Judaism, not its own religion. It was only after the revolt was put down, when they tried to distance themselves from the (now hated) Jews, that Christianity started to become its own distinct religion (save for Paul, but he was more or less shunned by the Christian community back in Palestine lead by James).
I both agree and disagree with you.
The bolded part is where I disagree, in only that Jesus being accepted as a Messiah would undoubtedly change how Jews view the whole idea of Messiah.
We have to keep in mind that during the 1st centuries BCE and CE, we are not really dealing with one form of Judaism, but Judaisms, depending on where you stand in the Jewish community and where you are in the Empire (if you are even inside it).
I mean, you have Pharisees (the proto form of Rabbinic Judaism) and their beliefs, the Sadducees (associated with the Temple cult and effectively destroyed following the revolt) and their beliefs, the Essenes, the revolutionary zealots, etc.
These people often had very different interpretations on how to interpret the Law and other matters. Of those groups and almost all the others listed, the only Jewish groups to survive the Revolt were the early Christians and the Pharisees.
And yep, the early Christians up to the revolt definitely were a Jewish sect, since they still followed the Law and worshipped in the Temple (though the claims of James worshipping daily in the Holy of Holies is dubious at best).
So if Jesus somehow leads to a successful enough revolt EARLIER, that is going to effect Judaism greatly. Judaism would not be the same, especially if there is no Christianity.
Christianity played a key role in the development of Rabbinic Judaism, if only to serve as the other (both Christians and Rabbis wanted to distance themselves from the other, and despised groups that stayed in the gray zone between them) and to pass oppressive laws (after the Imperial conversion)that caused Judaism to go from a accepting evangelizing religion. to an ethnic one.
The theology of modern Judaism evolved after the Revolt in reaction to events, and even the concept of Messiah was up in the air in terms of interpretation. I mean, it was only with the creation of the Talmud that Rabbinic ideas of the afterlife were settled as well.
In the first century, the idea of a Divine Messiah was accepted among various groups within Judaism, not just Christianity. There was of course the second concept of the Royal Messiah, who would actually lead the armies and restored the Kingdom of David.
Jesus was very much fitting into the mould of the first idea, but it wasn't new to him or others. Some people of both groups converted to Jesus' movement (while never seeing themselves as converting), but many from both groups did not. The Royal Messiah people for obvious reasons, and people who believed in a divine Messiah for the simple reason they didn't see Jesus as that Messiah.
When Rabbinic Judaism took a firm hold, they effectively killed the idea of a Divine Messiah and settled fully on the Royal Messiah.
SO...
if Jesus leads a very popular revolt, and it is crushed, its going to have knock on effects on Judaism all the way down the millenia. What beliefs did they have of Jesus? How do they interpret the crushing of the revolt? What happens to the Temple cult? If it is destroyed, do the Pharisees succeed in defining Judaism along their lines?
It all sort of depends.