Using Themekey to configure a Theme, without changing your visible, default Theme
You can change your site to a different Theme, that only you can see, when logged into your account. This allows you to prepare a different Theme, while still displaying your current Theme to customers.
Choosing the Themes that you want to work with:
First, you'll need to visit the list of Themes, and make sure you enable any that you might want to use. Click "Appearance" in the top, Admin menu bar.