You can edit most everything, but we recommend handling the following with caution: 

You don't want to delete any data-collecting fields off your live page. This can negatively impact your reporting. 

If you need a field removed, we recommend using a date-based action instead: 

After publish, you cannot edit - 

If you update your page's subdomain, you will have to re-publish the page. This will direct any linked / bookmarked versions using the old URL to a 404 error, so be sure to update any website or social media post using the old URL with the new URL. 

Any registrations taken from the old URL are still valid after the update. 

Once you share (whether through preview or live mode), Facebook will memorize whatever was initially shared by your page, even if you update what is appearing in the Social Media tab. You can update this image in the Social Media tab.

You might need to debug the image. 

Once your Registrants have claimed their account on the live page, they will be able to return to your account URL and view their registrant information, even if you disable Registrant Permissions on the form. 

If needed, you can update the dates so they won't be able to edit their orders.