Change the question "closeable" attribute using an advanced theme

Question

Goal: Only experts, moderators and admins shall be able to close questions

My attempt in qa-theme.php without checking the privileg, just trying to remove the close button:

        // abstract method: first and safest place to change content and layers
        function initialize()
        {
            // QUESTION page
            if($this->template=='question') {'
                // $this->content['q_view']['raw']['closeable'] = false;
            }
            // ...

The effect: closable is set to false, but the close button still appears.

Guess I need to override the button output funtion and to the check there?

Comments

Okay, I was able to remove the close button:
unset($this->content['q_view']['form']['buttons']['close']);

But I would really like to know how to use the closeable boolean above (!)