I think to change Hitlers antisemitism we have to go another way, he need to marry a Jewish girl. Why do I suggest this? Not because I think a single Jew would make a difference, but it would make it more likely for Hitler to interact with her family and friends, and interact in more intimate setting than between friend. He would join them at holiday dinners, meet many different kind of Jews, this would make it much harder for Hitler to look at a individual Jew he liked as a virtuous exception. He could still be a hateful nationalist, Jews are just not on the target list anymore.