This is a serious omission for Grace Themes. Website developers duplicate websites to create new design looks so it does not impact the live site. When the new design is ready to go live, they simply copy/replace the theme files on the live site, export/import theme database records, then activate the theme so the new design is live.
When you have active eCommerce websites with 24/7 sales being processed, you can’t replace the live site with the development site as sales data will be lost.
This inability has me in a tough situation with a client website.
I highly recommend that you create an export/import functionality on your Themes.