Here is what worked:
add_action( 'after_setup_theme', 'parent_override' );
function parent_override() {
unregister_sidebar('sidebar-4');
/** I have looked for the ID of the sidebar by looking at
* the source code in the admin.. and saw the widget's id="sidebar-4"
*/
register_sidebar(array(
'name' => 'Footer',
'before_widget' => '<div class="span3">',
'after_widget' => '</div>',
'before_title' => '<h6 class="footer-widgets-item">',
'after_title' => '</h6><hr>',
));
}
It seems that the id is not a slug of the name, and if you did not specify an id upon registering the sidebar, it will have an id of “sidebar-#”…