Change the Slug of Post Type post to baseurl/post/%postname%

I have been searching around but i cant anywhere find the answer to my question: How to change the post slug for all posts (and the categories etc.). Without affecting other pages/ custom post urls.
So i want to change the url for default posts from:

url/postname > url/news/postname

Without affecting page urls and or custom post type urls. The only method i have so far found that achieved what i was looking for was:

http://wordimpress.com/how-to-add-a-custom-permalink-structure-for-only-the-wordpress-default-post-type/

add_action( 'init', 'my_new_default_post_type', 1 );
function my_new_default_post_type() {

register_post_type( 'post', array(
    'labels' => array(
        'name_admin_bar' => _x( 'Post', 'add new on admin bar' ),
    ),
    'public'  => true,
    '_builtin' => false, 
    '_edit_link' => 'post.php?post=%d', 
    'capability_type' => 'post',
    'map_meta_cap' => true,
    'hierarchical' => false,
    'rewrite' => array( 'slug' => 'post' ),
    'query_var' => false,
    'supports' => array( 'title', 'editor', 'author', 'thumbnail', 'excerpt', 'trackbacks', 'custom-fields', 'comments', 'revisions', 'post-formats' ),
) );
}

By re-registering the post type. But this also has the side effect that it creates a second menu item on the left side of the admin panel called post. They both contain the same data though.

Hopefully somebody has an answer to this problem.