Yes, you can continue to update and edit your site at any time even if the event is activated or live.
Our recommendation is to not change the event URL once the event has been activated or sent to participants. This will make the original link invalid and will be confusing for those who were previously invited. Otherwise, you can change any details on the site and it will be updated instantaneously.
To edit your event once it has been updated, just make the changes on the backend and make sure to hit "update" or "save and continue" then navigate to the "review and publish" section of the page. Make sure to hit publish! This will update your activated page.