Простой способ для пересчета стоимости заказа после его изменения

msOrder

<?php
class msOrder extends xPDOSimpleObject
{
	public function updateProducts()
	{
		$originalContext = $this->xpdo->context->get('key');
		$this->xpdo->switchContext($this->get('context'));
		$originalMiniShop = isset($this->xpdo->services['minishop2']) ? $this->xpdo->services['minishop2'] : null;
		$cart = array();
		foreach ($this->getMany('Products') as $product) {
			$product = array(
				'id' => $product->get('product_id'),
				'price' => $product->get('price'),
				'weight' => $product->get('weight'),
				'count' => $product->get('count'),
				'options' => $this->xpdo->fromJSON($product->get('options')),
				'ctx' => $this->get('context'),
			);
			if (!is_array($product['options'])) {
				$product['options'] = array();
			}
			$cart[md5($product['id'] . $product['price'] . $product['weight'] . $this->xpdo->toJSON($product['options']))] = $product;
		}
		$address = $this->getOne('Address');
		/**
		 * @var miniShop2 $miniShop2
		 */
		$miniShop2 = $this->xpdo->services['minishop2'] = new miniShop2($this->xpdo, array(
			'cart' => $cart,
			'order' => array_merge($address ? $address->toArray() : array(), $this->toArray()),
		));
		$miniShop2->initialize($this->get('context'));
		$cartStatus = $miniShop2->cart->status();
		$deliveryCost = $miniShop2->order->getCost(false, true);
		$this->fromArray(array(
			'cart_cost' => $cartStatus['total_cost'],
			'weight' => $cartStatus['total_weight'],
			'delivery_cost' => $deliveryCost,
			'cost' => $cartStatus['total_cost'] + $deliveryCost,
		));
		$this->xpdo->services['minishop2'] = $originalMiniShop;
		$this->xpdo->switchContext($originalContext);

		return $this->save();
	}
}

Предлагаю модифицировать этот способ, чтобы он не требовал изменения кода. Кроме того, работал бы не только при обновлении товаров, но и при изменении способа доставки.

Создаём плагин на событие msOnBeforeUpdateOrder:

switch ($modx->event->name) {
    case 'msOnBeforeUpdateOrder':

        $originalContext = $object->xpdo->context->get('key');
        $object->xpdo->switchContext($object->get('context'));
        $originalMiniShop = isset($object->xpdo->services['minishop2']) ? $object->xpdo->services['minishop2'] : null;
        $cart             = array();
        foreach ($object->getMany('Products') as $product) {
            $product = array(
                'id' => $product->get('product_id'),
                'price' => $product->get('price'),
                'weight' => $product->get('weight'),
                'count' => $product->get('count'),
                'options' => $object->xpdo->fromJSON($product->get('options')),
                'ctx' => $object->get('context')
            );
            if (!is_array($product['options'])) {
                $product['options'] = array();
            }
            $cart[md5($product['id'] . $product['price'] . $product['weight'] . $object->xpdo->toJSON($product['options']))] = $product;
        }
        $address   = $object->getOne('Address');
        /**
         * @var miniShop2 $miniShop2
         */
        $miniShop2 = $object->xpdo->services['minishop2'] = new miniShop2($object->xpdo, array(
            'cart' => $cart,
            'order' => array_merge($address ? $address->toArray() : array(), $object->toArray())
        ));
        $miniShop2->initialize($object->get('context'));
        $cartStatus   = $miniShop2->cart->status();
        $deliveryCost = $miniShop2->order->getCost(false, true);
        $object->fromArray(array(
            'cart_cost' => $cartStatus['total_cost'],
            'weight' => $cartStatus['total_weight'],
            'delivery_cost' => $deliveryCost,
            'cost' => $cartStatus['total_cost'] + $deliveryCost
        ));
        $object->xpdo->services['minishop2'] = $originalMiniShop;
        $object->xpdo->switchContext($originalContext);

        return true;

        break;
}

Т.е. в Вашем коде $this теперь заменён на $object