Installing Theme on Site With Live Data

I'm attempting to install the Evolve theme on a site that already has Drupal installed and already has data, including custom data types. I would like to install the theme with the demo data.

I see that you have recommended the "Full Installation" in other threads that ask this question. However, it seems that following those directions would disconnect my site from the database and data that already exist.

Is there a way to install the demo on a site that already has live data without disconnecting from the already existing database?

I'm assuming this would involve

• installing any modules required by the theme that aren't already installed
• creating database tables required by the theme that don't exist
• importing theme demo data

Are there other steps? Anything I need to make sure I don't miss?  Is this possible?