It's going to be just like any goodwill policy. Airlines will assess the situation, make a decision on who can benefit from booking / rebooking, etc.
If you want to preemptively change your booking, you may, but you might be stuck with the bill.
Do note two things:
- Once IROP hits your flight, you can change to any airline etc, but before that it is all goodwill and AC will likely force you to stay on AC
- FL is garbage when hurricane hits, you will see all flights will go Y0 on all Airlines. Check OFTEN. There will be thousands of people booking cancelling and changing flights nonstop for the next week. Things will be extremely dynamic. Airlines usually uplift some sections on the day before. I think a few years ago on one of the big hurricanes AC added what, 5 or 6 777 flights? All pulled out of maintenance and running on MELs the length of public stall single ply toilet paper, but the uplift was there.
- DON'T BE OVEREAGER. A confirmed flight 2-3 days AFTER the hurricane is much more reliable than a flight on the day it will start or the day before. You may push and try hard for that flight, but once it will get cancelled you will have no space on any airline for DAYS (maybe a week), and you will have to wait for the hurricane to finish before the Airlines can schedule and crew extra sections.