You may find it easier to cheat and run your script with
and rt_site_config.pm doesn't declare any of your ExternalAuth
Also, pelase note that AutoCreate only comes into play for users
created in the WebUI, so is irrelevant here. Also,
AutoCreateNonExternalUsers is an RT-Authen-ExternalAuth config option
and is irrelevant if you're disabling RT-Authen-ExternalAuth.
If you don't want a second site config, you'll need to ensure that
your config changes happen before RT loads and parses plugins.