/**
*   WooCommerce woocommerce_order_item_line_item_html action hook registeration.
*/
add_action('woocommerce_order_item_line_item_html', 'woocommerce_order_item_line_item_html', 1, 3);


/**
* Callback Listener for customised line item functionality in the admin.
*/
function woocommerce_order_item_line_item_html($item_id, $item, $order){
    // Add your custom line item functionality.
    // A good example would be order fulfillment for a line item.
}