Airlines are reluctant to change bookings made by other airlines. This wouldn't be a problem if you have a travel agent who knows what they are doing. And they would effectively make 2 bookings for you. 1 to issue the ticket, and another with just your reservations.

Airlines also have a tendency to place "NVB/NVA" dates on the tickets and even making date changes will be problematic. (NVB-Not Valid Before/ NVA-Not Valid After)