EventNook allows the deactivation of the event registration site whenever you need it.
To deactivate the event,
Go to My Events >> Manage
Click the Live button's dropdown menu on the top right of your page.
Click Deactivate Event
Then, click Confirm to proceed.
Follow the popped-up URL or your event URL, and you can view that your event page has been deactivated.
If you want to make the event registration site Live again, you can click Make Event Live to publish the event page again.