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

You don't want to delete any data-collecting ticket levels or 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 all your pages. This will direct any linked / bookmarked versions using the old URL to a 404 error. 

If you update your pages's URL, both the old and new URL will stay valid. But only if you've already accepted registrations on the original one. 

Once you share (in preview or in live mode), Facebook will memorize whatever was initially shared by your page. Even if you update what is appearing in the Social & Sharing tab. 

You might need to debug the image.