Restore canceled order with Magento 1.x

undo_cancel.php

<?php
// -------------------------------------------------
// Prevent script to be called via HTTP
// -------------------------------------------------
if (isset($_SERVER['REQUEST_METHOD'])) {
    die('This script cannot be run from Browser. This is the shell script.');
}

// -------------------------------------------------
// Override useful ini values
// -------------------------------------------------

set_time_limit(0); // avoid any time limit
ini_set('memory_limit', -1); // avoid any memory limit

// -------------------------------------------------
// Include Magento Core
// -------------------------------------------------

require_once 'app/Mage.php';

// -------------------------------------------------
// Load and Start Magento Application runtime
// -------------------------------------------------

// Trick reference:
// http://www.magentocommerce.com/boards/viewthread/38379/#t189142
Mage::app()->setCurrentStore(Mage_Core_Model_App::ADMIN_STORE_ID);
umask(0);

// -------------------------------------------------
// Init an admin user session
// -------------------------------------------------

$userModel = Mage::getModel('admin/user');
$userModel->setUserId(0);
Mage::getSingleton('admin/session')->setUser($userModel);

$orderId = 14;

$order = Mage::getModel('sales/order')->load($orderId);
foreach ($order->getAllItems() as $item) {
    /** @var Mage_Sales_Model_Order_Item $item */
    $item->setQtyCanceled(0);
    $item->setTaxCanceled(0);
    $item->setHiddenTaxCanceled(0);
    $item->save();
}
$order->setSubtotalCanceled(0);
$order->setBaseSubtotalCanceled(0);
$order->setTaxCanceled(0);
$order->setBaseTaxCanceled(0);
$order->setShippingCanceled(0);
$order->setBaseShippingCanceled(0);
$order->setDiscountCanceled(0);
$order->setBaseDiscountCanceled(0);
$order->setTotalCanceled(0);
$order->setBaseTotalCanceled(0);
$order->setState(Mage_Sales_Model_Order::STATE_PROCESSING, true);
$order->save();