Creating a New Child Theme from Main Site

I am using the Blogs MU template from here and I have a question. When I first created my main site I did NOT create the home page using a childs theme. (Mistake I know)
Now I need to update the Blogs MU default theme but I know when I do I am going to lose some if not all the work I have done to this point.

My question is, I want to use the "New Blogs Templete" to recreate the main site and all the post, pages, etc... that go along with it.

I have been reading the Create a New Blog Template but I am unsure if I can clone the main site and set it as a child theme so I can update the BlosMU Theme and not lose my settings.
I am pretty sure I can do this but dont know how...
I want be sure about this before I start this process...
Thanks for your help.