creditmemo.php

<?php

require_once 'app/Mage.php';
Mage::app();

/** @var Enterprise_Rma_Model_Rma $rma */
$rma = Mage::getModel('enterprise_rma/rma')->load(135215);

$qtys = array();
/** @var Enterprise_Rma_Model_Item $item */
foreach ($rma->getItemsForDisplay() as $item) {
    $id = $item->getData('order_item_id');
    $qtys[$id] = $item->getData('qty_approved');
}

$data = array('qtys' => $qtys);

$orderId = $rma->getData('order_id');
$order = Mage::getModel('sales/order')->load($orderId);

/** @var Mage_Sales_Model_Service_Order $orderService */
$orderService = Mage::getModel('sales/service_order', $order);

/** @var Mage_Sales_Model_Order_Creditmemo $creditMemo */
$creditmemo = $orderService->prepareCreditmemo($data);
$creditmemo->setOfflineRequested(true);
$creditmemo->register()->save();

// Save creditmemo and related order, invoice in one transaction
$transactionSave = Mage::getModel('core/resource_transaction')
    ->addObject($creditmemo)
    ->addObject($order);
if ($creditmemo->getInvoice()) {
    $transactionSave->addObject($creditmemo->getInvoice());
}
$transactionSave->save();