Hi everyone
I successfully changed my ticket to the 28th, NRT-LAX-SFO. I think maybe the original AA representative was having a bad day or just didn't know how to handle my request as she was adament it would be impossible to change flights. I had very little trouble when I called today and was speaking to a different lady. There was no need for pleading! I'm going to ring again tommorow and confirm that my tickets are reserved.

Thank you everyone who helped me!