I agree that the disabling of nodes for monitoring would be a helpful feature. We often have nodes which are down for utility work on a campus building or other types of planned service.
Originally, we had a home-cooked polling system which had a "no call list." It was a separate, viewable report of the nodes for which polling was disabled. The separation of the report allowed us to test those nodes periodically in case they had been missed for removal from the list.
The lack of such a feature has the effect of muddling up the list of down nodes when we have such planned outages, and the appearance of a new node has a vastly-reduced chance of being noticed, especially had no other nodes been on the down report (in the ideal situation).
