I've seen a few tutorials like this one explaining how to move a store from a test site to a live site. But all these steps seem to be focused on a one time setup but are a lot of work if I'm making frequent changes over time.

Is there a way to make changes on a test site, say on my PC (I've got a local test site already set up) and then publish only the files that have changed?

For example, I suppose if I only made a change to C:\xampp\htdocs\zencart\includes\templates\custom\css\stylsheet.css, I could just FTP that to the appropriate location on the live site.

But what if I made a LOT OF CHANGES? And what if I make changes through the admin panel? (those settings are saved in the mysql db, right?). How would I upload those changes and avoid overwriting any new customers/orders that came in while I was working on the test site?

So, maybe what I'm asking simply, is there a way to upload just admin/structural changes and not affect the customer/order information that comes in. Something that would allow for a lot of development on a local test site and then frequent updates to the live production server.