I have succeeded in adding some extra custom fields to the edit question form via a plugin layer.
However, when you save the question after editing it, the code in the core (qa-page-question-post.php on lines 119 - 122) runs qa_page_q_edit_q_submit() and then immediately redirects to the question with qa_redirect(). The redirect makes it impossible to save my new extra fields information to the database.
I have commented out the qa_redirect() in the core and added a if (qa_is_http_post()) to my layer and then new information is saved without a problem.
However, I do not want to change the core. How can I ensure that the new fields are processed correctly without changing the core when I submit the form? What can I add to my layer to have the new fields I have added get processed before there is a redirect?