update_user_meta on registration but only for default role type

Here is what you need to do:

function set_user_rcp_default_subscriber($user_id) {
    $user = new WP_User( $user_id );  

    foreach( $user->roles as $role ) { 
         if ( $role === 'subscriber' ) {
              update_user_meta( $user_id, 'wp_user_level', '0' );
              update_user_meta( $user_id, 'rcp_subscription_level', '1' );
              update_user_meta( $user_id, 'rcp_status', 'active' );
              update_user_meta( $user_id, 'rcp_expiration', '2014-06-30' );
         }
    }
}

add_action("user_register", "set_user_rcp_default_subscriber", 10, 1);

We need to loop through it because potentially a user can have multiple roles.