WordPress Automatic Filename Changer

The add_attachment action is called after the attachment has been named. If you only want to change the name of the attachment (and the slug), you don’t need to change the name of the file and can just replace the code inside rename_attachment with a call to wp_update_post.

add_action('add_attachment', 'rename_attacment');
function rename_attacment($post_ID){
  $new_attachment_name = array(
    'ID' => $post_ID, 
    'post_title' => $post_ID, // changes what you see 
    'post_name' => $post_ID // changes the slug to 89
  );

  wp_update_post($new_attachment_name);
}