unapprove comments on custom post type

You should be able to write a function that fetches all comments by comment type using get_comments(), then loop through them and set status using wp_set_comment_status().

e.g.

Retrieve all comments associated with posts in the debate post type:

$debate_comments = get_comments( array( 'post_type' => 'debate', 'status' => 'approve' ) );

Loop through each one, and change from approved to moderated:

foreach( $debate_comments as $debate_comment ) {
    wp_set_comment_status( $debate_comment, 'hold' );
}