Originally Posted by anabolism

If you want to change your routing, then you need to wait until after you've flown at least the first flight. If you only change date/time/carrier on flights other than the first, then you can do that before the trip starts. I do this all the time: book a trip for 11 months in the future, with real dates for the first few flights, and dummy dates for the rest. Five or six months after ticketing (still several months before the first flights), call to change the dummy dates to real ones.