by Davo Smith.
You could try looking in mod/assign/locallib.php, function notify_grade_modified.
That currently sets mailed to 0 (ready to send mail) ONLY if the flag isn't already 1 (mail already sent).
You could remove the if ($flags->mailed != 1) condition and see what happens, but I assume it is there for a reason, so I'd make sure it was carefully tested before deploying to a live site.
