feeds integration?

Here's an example in case someone ever wants to take this on https://www.drupal.org/project/geofield/issues/2969120 →

This is a lightweight module to add a simple heading-level option to a text or string field.

There are different modules who provide hooks or event subscribers to format/manipulate/include/... other modules content or configuration.

I'm not gonna include feeds support in this module. The example code suggested in comment #2 can be used in case you need to add the heading output into the feeds module.