Thanks all for the replies

So if Cathay is the issuing carrier, I call Cathay to add segments (once I've started travel)?

Sorry, for another basic question, how complicated is it to call the issuing carrier? Does it take a long time on the phone to sort out? and do the changes get effected immediately? Can I call AA instead of Cathay (if yes, will the general number work or is there a special number?)

Might not be worth the additional headache of being on hold with Cathay for two hours in the middle of the night...

Thanks again