Guys, thanks so much for all your help. I am 'terrifically excited' to be able to tell you that I was able to change to a flight one day earlier (with a return one day earlier as well) going through Chicago instead of San Francisco. Hopefully my ORD-NRT flight will stay with a 747! The United rep was very helpful and even though he had to change the routing, he did not charge me a change fee.

Thanks so much--I love FlyerTalk!