If you are reading this idea suggestion, I hope it is not too late for you. Why allow the user to change the authentication method once the install is completed? What are the options to solve this?
One option would be to grey-out the "Authentication Type" section in the "Gallery Authentication" screen, so the user is not able to change authentication methods once after the first configuration is set. This would still allow the user to change SAML settings.
Another option, if somehow there is a reason why a user would want to change authentication types even though it is not supported, what about changing the layout to make it more difficult to change the authentication type.