Superadmin Sites

I have a new 3.0.1 install and have successfully enabled the multisite functions. I can’t find any information about the superadmin options on the Sites tab in the admin.

There is Site Info where Domain and Path are editable.
There is Site Options where Siteurl is editable.

My main site is base.html The secondary site is base.html/site1

I want to set a different url to resolve to site1. I have set my dns records for site1.html to point to this server. My questions are about the superadmin settings above. Can I change them to make this work or do I need to use the domain mapping plugin? And what happens if I change these in the superadmin?