Yeah, you should be able to do that. Open your core/modules/Screenshots/Screenshots.php file and find the following statement:
ScreenshotsData::send_message($who_to, $who_from, $subject, $message);
There should be two of these statements in the above mentioned file. One of them is within the "approve_screenshot" function and the second one is within the "reject_screenshot" function. Below the above mentioned statement you can add the following:
$pilotdata = PilotData::getPilotData($who_to);
$subject = "Screenshot Approved or Rejected";
$message = "Congratulations, you screenshot has been approved. etc";
Util::SendEmail($pilotdata->email, $subject, $message);
You can update any of the above variables (subject or message) to send the right message for "reject_screenshot" too. You can also comment out the statement that exists to send the airmail to the pilot like this:
//ScreenshotsData::send_message($who_to, $who_from, $subject, $message);