Programmatically disabling webform component - Drupal 7
I have never had luck trying to set the disabled flag via a FormsAPI hook using the array indexes.  Looking at the code above, it would also seem that you are setting the incorrect 'disabled' for the form array - #disabled is what is checked during the rendering process.

But, like I said, never had much luck with it anyway.  What you may end up needing to do is set the #attributes array for the form element, specifically identifying the disabled property as in the html element tag:

&lt;input type='text' disabled /&gt;
// becomes
$form['element']['#attributes'] = array('disabled' =&gt; '1');


obviously with the form indexes specified as needed.