The word "cannot" should NEVER be in an admin or someone with responsibility's vocabulary.
Someone obviously programmed this, so someone can obviously turn it off.
Anyway - to answer question #1:
There is a piece of code in this file projects/application/models/notifier/notifier.class.php
on approx line 43 which has:
else if ($action == ApplicationLogs::ACTION_TRASH) {
self::objectNotification($object, $subscribers, logged_user(), 'deleted');
I simply commented out this else if statement....
Not sure if it does the trick yet - I'm waiting on someone to send something to the trash first to see. But this should disable it.
Alternatively, you can add a column to your database that sees whether the user wants to be notified and then change this else if to something like this:
else if ($action == ApplicationLogs::ACTION_TRASH && $wants_notified) {
self::objectNotification($object, $subscribers, logged_user(), 'deleted');