So far, so good!
I added everyone to a group called "Jury Room," and gave that group permission to post in here. Then I switched off the individual posting permissions for all the old members. As long as you're members of the Jury Room group, you have posting permission here. When you leave the group, or when the committee is finished, all the admin has to do is remove the name(s) from the Jury Room group. New members of the committee will just have to be added to the group, and their permissions are on.
No more hand switching of permissions!
(Please pardon the admin geekout.
Consider it a Teaching Moment for the committee's four admins-elect.)