Originally Posted by rsteinmetz70112

Being checked-in does not affect the ability to rebook.

I rebooked well inside 24 hours a couple of weeks ago. If you rebook on an earlier flight after being automatically assigned a boarding priority that priority may suffer. If you rebook a later flight outside the assignment window your priority should hold. It did for me a couple of weeks ago when I rebooked a later flight. However as with all things Southwest YMMV.