Assign published posts to another user automatically

You can try using wp_insert_post_data for the task. Something like:

function assign_new_post_to_specific_author( $data , $postarr ) {

  // Where author_ID is the ID of the author you want to assign the new post
  $data['post_author'] = author_ID; 

  return $data;

}

add_filter( 'wp_insert_post_data', 'assign_new_post_to_specific_author', '99', 2 );

Tried it on c9.io and it works, but you need to check the filter priority for yourself.