This is a brilliant feature in WordPress.
1. Go to General Settings.
2. Change your WordPress Url
3. Click Save Changes.
You won't get a warning - all you will get is a blog without any CSS and without anyway to login. Not bad. Great idea! Even Microsoft is not that clever.
oh..for the poor idiots like myself who actually thought they could test a setting without destroying their blog: find the url record in the proper database table and set it back to the original state.