GIVEN I have a document with subrefs
WHEN I click on a subref footnote marker
THEN I see the context Item with two edit buttons, one for the main and one for the detail

The top edit button will now edit the main ref, and the bottom edit button will edit the subref. In order to edit the main ref, the callback probably needs to select the main ref footnote body in the same way as if the user had clicked in the reference list to edit it there. We can't assume the main ref has its own footnote marker. The edit reference dialog is designed to work on the selected text.