Which your Elgg version?

Since Elgg 3 we use Doctrine DBAL for SQL queries.

V 4.3.7

Try this:

$name = get_input('name', '');
$query = get_input('query', '');

echo elgg_list_entities([
     'types' => 'user',
     'metadata_name_value_pairs' => [
          [
                 'name' => 'usertype',
                 'value' => 'driver',
          ],
     ],
     'joins' => [
          new \Elgg\Database\Clauses\JoinClause('metadata', 'em',             function(\Elgg\Database\QueryBuilder $qb, $joined_alias, $main_alias) {
          return $qb->compare("{$joined_alias}.entity_guid", '=', 'e.guid', ELGG_VALUE_INTEGER));
         }),
     ],
     'wheres' => [
           function(\Elgg\Database\QueryBuilder $qb) use($name, $query) {
              return $qb->merge([
                         $qb->compare('em.name', '=', $name, ELGG_VALUE_STRING),
                         $qb->compare('em.value', 'LIKE', '%$query%', ELGG_VALUE_STRING),
               ], 'AND');
            },
      ],
      'limit' => 5,
]);

On your questions:

1 - Why not? Just use a new way ;)

2 - Absolutely if you follow Elgg's code standards.

3 - Look at my example and the existing core and plugins' code. Ask here or welcome to Elgg chat in Telegram. We've a channel also.

For now you could set the logged in user during the script.

$session = elgg_get_session();
$session->setLoggedInUser($user);
$session->remove('guid');

// actions

$session->invalidate();

This "logs in" $user as far as Elgg is concerned, but prevents the GUID from being stored in the session.

If a browser hits this script, and actions fail, there'll be less chance that the browser would be left in a logged in state.

Note that anybody on the web can call your /cron triggers!

That worked steve. Thank you.

Why cant we use the owner_guid as the notifying user's guid value in such situations?

@aqeel See my comments on GitHub.