I've had mixed results. In a situation earlier this year with some similarities (weather predictions much worse, but I was still asking for a proactive resolution to a hypothetical misconnect), I got an agent who felt I was doing AA a favour by rebooking. I ended up with a flight a day later, routed through another city, with SWU upgrades intact without even asking. However, I've also been told to wait it out, as if the weather is very bad, many others will quite possibly misconnect as well, leaving seats free on those flights now showing full.

What was the time variation of the schedule change? Significant?