Originally Posted by hurnik

AA's system may not let you book the new one (it wouldn't let me do it for the same itinerary at lower prices). I had no choice but to cancel the current one and cross my fingers/hope that I could still book at the lower price. You can open two browser windows (different browsers) to try to make things as quick as possible.

Supposedly the other option is to hold the new itinerary (again, AA's site won't let you do this) without somehow attaching your AA account # to it. Not sure how one puts an itinerary on hold with miles without their AAdvantage #, but apparently it's possible.