Originally Posted by Droopy

The short answer is there are only two docking ports on the ISS compatible with Crew Dragon/Starliner. The Crew 8 Crew Dragon spacecraft is currently on the other port. It's the emergency "liferaft" for the current Crew 8 astronauts onboard. For safety reasons, you can't undock it without them going with it. Since the reprogramming isn't a quick process (I heard in the neighborhood of 4 weeks), you can't play chess and undock Crew 8 with them onboard, dock Crew 9, quickly reprogram and undock Starliner, then redock Crew 8 where Starliner was.

You could potentially have Crew 8 depart before Crew 9 arrives, but I suspect that would have profound ramifications on the various station maintenance schedules and ongoing science as you wouldn't have enough people onboard to do everything required...