[2020 Pandemic Date Specific] Emergency Policy Manual

As we look to re-opening our public libraries with abridged services, we want to limit the chances of legal challenge from organizations who seek to make a statement about government response to COVID-19 and social distancing measures. We are considering a recommendation to have a brief policy manual addendum with policy adjustments that supersede the policy manual, have a short review and renew period (aligned with the library board meeting schedule), and are triggered by an objective, external to the library, event. What elements would we need to include in this addendum to make it legally enforceable, while not re-writing the entire policy manual?

Take, for instance, a library's meeting room policy. For a library with a 2,000 sq ft community room, with a normal occupancy of 250 persons and a seated occupancy of 150 persons (fake numbers), in which the board meets every other month.
- Initial addendum policy would have a line which said "Meeting Room: The meeting room is closed to all groups. Policy approved April 27, 2020. Will expire June 26, 2020."
- At the June board meeting the board passed "Meeting Room: The meeting room will open for library sponsored programming July 1st. Registration will be required and limited to 20 persons to follow current social distancing guidelines. Policy approved June 26, 2020. Will expire August 27, 2020."

And so on.

What are recommendations for the pre-amble of such an addendum? What should we make sure to include in the board motion to enact the emergency policy addendum such that it supersedes the standard manual?