Unenrolling is not the same as blocking. Blocking can only be done internally by edX. In January, I was told NOT to document the concept of blocking, as access to the PMs is not available to all possible users of the platform. I agree that changing the course enrollment end date is probably not feasible in many cases, however, I was told that since students can and do immediately re-enroll themselves after being unenrolled, course staff should know why that is possible and be forewarned about it.
@mhoeber, adding to DOC-270 to be sure to involve product in revisiting the way this is positioned.