Got it. I think we’re happy with new users receiving notifications for this topic (since there will be no new users for another few months).
Looking at the code, it seems Topic.find(id).topic_users.update_all(notification_level: 0) will do the trick. Can anyone confirm?
0 appears to be the muted state according to this code: discourse/app/assets/javascripts/discourse/lib/notification-levels.js.es6 at c6ff387ce9d7660c804e9ba55096167dc427a751 · discourse/discourse · GitHub