I’m running into a similar situation.
I have a flexible content field (tabbed_content repeater) that allows the user to add a Tab Content section, and add tabs via a repeater.
When they add a new post I’d like to be able to ‘auto populate’ that page with a tabb_content element, but still allow them to add/remove tabs (which is a repeater as mentioned).
Is there any way to programmatically add this flexible content item of tabbed_content, with a predefined set of tabs..?