You can easily create different versions of your book by making modifications to your existing theme. Here's how:
Click on the three dots next to the theme name that you want to modify.
Select 'Duplicate' from the options provided.
Rename the duplicated theme to specify the version you want to create.
Make the necessary adjustments to the duplicated theme.
Once you have customized your theme for the specific version you need, you're all set to export it. When you're ready to export your different versions, simply select the desired theme for each version, and then hit the export button.