Я решил проблему:
require_once 'app/Mage.php';
Mage::app('');
$attribute = Mage::getModel('eav/config')
->getAttribute('catalog_product', '955');
foreach ( $attribute->getSource()->getAllOptions(true) as $option){
//here comes the code sample (see link before)
.
.
.
$product->setMyCustomAttribute($option['value']);
}