The annotation @export_range() already has support to show the value as degrees in the editor but store it as radians in your exported variable.
Most common exports are already covered by the other @export annotations but if you need something more specific you can use the annotation @export_custom() which let you export a variable with custom settings.
If you need even more configuration or dynamic exports then you’ll need to use Object._validate_property() or Object._get_property_list(). Here’s an example on how to export the project’s input map actions Selector Plugin hinting issue - #3 by mrcdk