WordPress make admin post as a different user by default. You should never post a admin user, so you do not expose the admin username to others. But it would be nice if you would have a script that sets the post author to another user anyway. Now you do.

Create a new plugin pluginauthor and add the following code to it. The following code will set post author to AUTHOR ID 2 if you are posting as an admin.

 * @package pluginauthor
 * @version 1.0
Plugin Name: Plugin Author
Plugin URI: http://www.lehelmatyus.com
Description: Changing the author id from 1 to 2
Author: Lehel Matyus
Version: 1.0
Author URI: http://www.lehelmatyus.com

function pluginauthor_set_author( $post_id ) {

  // If this is just a revision, don't do anything.
  if ( wp_is_post_revision( $post_id ) )

  //Check it's not an auto save routine
  if ( defined('DOING_AUTOSAVE') && DOING_AUTOSAVE ) 

  //Perform permission checks! For example:
  if ( !current_user_can('edit_post', $post_id) ) 

  // If post author is admin -> set it to author id "2" 
  // special user set up for this purpouse
  // unhook this function so it doesn't loop infinitely

  if ( is_super_admin() ) {
    // if ( isset($_GET['auth_id']) ) {
      $args = array('ID'=>$post_id, 'post_author' => 2 ); // put ID of Default Author here
      wp_update_post( $args );
    // }

  // re-hook this function
  add_action( 'save_post', 'pluginauthor_set_author' );


add_action( 'save_post', 'pluginauthor_set_author' );


Be sure to change 2 to the default user ID you want to use a different one.

The above code is released under MIT License.