We ran into this when the OLGA AR was removed a while back. There was no way on mason (nor afaik on NGS, yet) to disable an AR without just entirely removing it. Esp with composition-data Recording ARs which really should be Work ARs, and need to be moved over manually, it would seem we'll have at least a few ARs which need some way to disable adding new ones, while still allowing existing ARs to be displayed, edited, or removed. The ability to flag an AR as "disabled; don't show this AR on the add page, or allow new ones of this type to be created" would therefore seem like something we'll find really useful to have in there.