Searching didn't yield anything recent/directly relevant with the "new" delta.

If I check in the Mrs's (she is FO) to her Y seat (not basic) can I change her seat later if a better seat opens up?

Will she still be eligible to get a C+ or F seat if that opens up before the flight today if she is already checked in?

In the past I was able to do this but not sure if this is still possible with the changes (read not enhancements) that delta has made.

Thanks