I have a website where I upload and sell T-shirts. I have about 50 or so designs up and they receive hits from Google.

I'm wanting to create a new T-shirt site where anyone can upload T-shirts and sell them. The database will be completely different from the old one. The purpose of the site is changing considerably but it's all still about T-shirts. I wanted to use the same domain name and keep the old T-shirt database and start integrating the new T-shirt DB. I would like to be able to use the rank I have with this site already as a stepping stone for this newer different T-shirt site version.

Will Google penalize me for changing the site too much? Or am I able to benefit from the rank and seniority my page has already for this different version of a T-shirt site. The domain will stay the same and the old T-shirts will stay on there (for now) but the theme of the site will change and more functionality will be added.