I was just able to change my flights SEA-DXB-NBO from J to F, 5 days before my outbound flight. @pjleitch, I was able to do it online for just the difference in miles--I didn't have to cancel/re-deposit. Excited to try both the 777-300ER and A380 in F (as posted previously, I'm coming back home through LAX).

And in case it's helpful to anyone: F availability has been coming online at AS.com almost every evening just after 9 PM Pacific for the SEA-DXB flight 5 days out.