Change author, disable comments, enable trackbacks for all items in library

Question

You have to run SQL query to do this. Put this code into your functions.php once, run your website and then delete it.

global $wpdb;
$author = 1;
$comment_status="closed";
$ping_status="open";

$query = sprintf(
    'UPDATE %sposts SET `author` = %d, `comment_status` = %s, `ping_status` = %s',
    $wpdb->prefix,
    $author,
    $comment_status,
    $ping_status
);

$wpdb->query($query);

Or run it directly from database (for example from phpMyAdmin):

UPDATE `wp_posts` SET `author` = 1, `comment_status` = 'closed', `ping_status` = 'open'

Of course you have to change author id to your author id and wp_posts to table name with your table prefix