What is the use of a TEST site in ChargeBee? Why can't I directly make changes in LIVE site and try them out?
If I make changes in TEST site will I be able to migrate the configuration changes to LIVE site without having to redo it?
And we support selective migration of product configurations from TEST to LIVE without any issues. You can navigate to LIVE site Settings => Copy sandbox data => Choose the specific configurations you want to migrate (plans, addons, coupons, email templates) and directly pull it into LIVE site.
Can you copy the data from production over to test?
Copying data from production to test is possible.
To get this done, in your test site, go to Settings > Site Settings and you'll find an option "Copy Configurations (LIVE to TEST)".
Clicking on this will let you copy configurations from live to test.
However do note that you'll be able to see this option only if you have a test and a live site. Here's a screenshot for your reference.