When I set up a campaign everything runs fine. But if I go back in and change the email content, the links contained in the emails are returning 404 errors. I see that each link is being stored in the database for tracking. Is there a best practice for changing email content on an existing campaign so that the new links (or changed old ones) will continue working? Or is it better to just delete the entire campaign and create a new one if/when the email copy needs to be changed?