This is a very helpful discussion, but I was hoping someone could help with the actual mechanics of doing this.

I just applied for the United Club Card (first year annual fee waived) and already have the AMEX Platinum Card with United selected as my designated airline for the airline credit.

When the first annual fee is charged for the United Club Card (presumably a year from now), the default will be to charge to the associated Chase Visa account .... to get the airline credit I have to have it charged to the AMEX and it has to appear as a United charge.

Is it as simple as just calling the United Club number as asking them to change the default annual fee billing account to AMEX? Will they be willing to do that? Will the charge appear to AMEX as a charge from United or a charge from Chase Visa?

Hopefully these aren't silly questions, but I was hoping those that have actually done this can give specific advice.
Thanks in advance.