Hello Madyson,
If you’re going to be creating a “sandbox website” and then bring them over to the live site, you’re probably creating more of a problem than a viable solution. If you are testing the update on a clone of your site, then running the same update on your live site, then it would make more sense and save your more time.
Based on what you’re asking, you want to make a duplicate of your site (it would have to run using a different URL than your main site), run an update on your clone, then move the updated clone into your live site – or at least the changes. This would require that you continually replace your live site with the updated clone. Moving ONLY the updates would be difficult unless you know where to update the files and database within WordPress.
When we think update in WordPress we’re thinking themes, plugins, database, or WordPress version. Please clarify what you’re updating and we can try determine the best way for you make sure it applies to your live site.
Kindest regards,
Arnel C.