Astra Pro Addon plugin provides Custom Layouts and Page Header addon. You can create custom designs with these addons.
Sometimes you might need to duplicate them, tweak a little and use again on the same or different sites. Below are some suggestions on how to proceed –
Duplicate Custom Layouts and Page Headers
You can use the external plugin for this. A plugin like Duplicate Page and Post allows duplicating Astra』s Custom Layouts and Page Headers. Just install the plugin, it will offer the option for each post.
Import / Export Custom Layouts and Page Headers
You can export Custom Layouts and Page Headers from WordPress backend under Tools > Export. Then Import it on another website from Tools > Import > WordPress ( Install > Run Importer ).