Remove anti-semitism from catholic doctrine (christ-killers was an alternative name for jews in the early days of the church). That would help in europe at least. It should reduce most of the restrictions that jewish communities operated under.
The shift could be initiated in the early 2nd century by theologians like Clement of Rome, Ignatius of Antioch, and Polycarp of Smyrna preaching and teaching more on the common heritage of Jews and Christians and on treating Jews with grace, mercy and friendship, saying things like, "they are our neighbors and spiritual kin, and even yet, God's beloved people. Similarly, John Chrysostom could have been about not speaking against Jews in general, when he denounced Judaizing Christians and those in his congregation who were taking part in Jewish festivals and other Jewish observances. Also, Augustine of Hippo could have spoken in greater depth about the connection between Christianity and Judaism when he spoke against groups within the Church who rejected the use of Hebrew Scripture.