No, if you move the first flight you will trigger a re-price. Lock the first date as far out as possible (usually 330 days) and put dummy dates for the remaining flights. The problem usually is that although the rules allow open dates for segments, I know AA (not sure about others) won't ticket without actual dates. So, that means the last flight, not the first, needs to be 330 days out. After the first flight you have 365 days to complete the trip.