Magento Test Area for not loosing customers data

I need to publish a ready magento ecommerce. But I want to make sono customization in the future. I would like to use a Test area to make all the customization that I want, and then update the official site. My doubt is, if I create a site/Test folder, and copy the DB from the official site, in this moment I lose all the future subscription and order from the DB copy. So when after some days, I ended my customization, new users have subscribed and new order have been placed. So if I import back the DB copied few days before, I lose those. How I need to proceed to avoid this problem and don't lose anything from customers and orders?