Magento customer migration from one instance to another even with version changes (max tested difference: mageCE 1.5 > 1.9)

customer_export.php

<?php

set_time_limit(0);
$pathTo = '../../';
$magentoFilename = $pathTo . 'app/Mage.php';
 
require_once $magentoFilename;
 
umask(0);
 
Mage::app()->setCurrentStore(Mage_Core_Model_App::ADMIN_STORE_ID);
 
$resource = Mage::getSingleton('core/resource');
$read = $resource->getConnection('core_read');
 
$addressfields = getAttributes(2);
 
$fieldnames = getAttributes(1," AND attribute_code !='default_billing' AND attribute_code !='default_shipping'");
$fieldnames[] = 'current_server_entity_id';
$fieldnames[] = 'addressess';
$fieldsCount = count($fieldnames);
 
$fp = fopen('customers.csv', 'w');
 
fputcsv($fp, $fieldnames);
 
$customerCollection = Mage::getModel('customer/customer')
                        ->getCollection()
                        ->addAttributeToSelect('*')
                        ->addFieldToFilter('website_id',array('eq'=>'1'))
                        ->addFieldToFilter('entity_id',array('gt'=>'1')); // entity id from 
 
foreach ($customerCollection as $customer) {
 
    $data = array();
    $addressData = array();
 
    foreach ($customer->getAddresses() as $address)
    {
        foreach ($addressfields as $field)
        {
            $data[$field] = $address->getData($field);
        }
 
        $data['default_billing'] =  ($customer->getDefaultBilling() == $address->getId());
        $data['default_shipping'] = ($customer->getDefaultShipping() == $address->getId());
 
        $addressData[] = $data;
    }
 
    $data = array();
 
    foreach ($fieldnames as $field)
    {
        $data[] = $customer->getData($field);
    }
 
    $data[$fieldsCount-2] = $customer->getId();
    //address data will be stored in the CSV which we can unserialize while exporting 
    if (count($addressData) >0)
    {
        $data[$fieldsCount-1] = serialize($addressData);
    }
 
    fputcsv($fp, $data);
 
    echo '<br>CustomerId: ' . $customer->getId();
}
 
fclose($fp);
 
/**
* Get Attributes 
* @param integer $typeId
* @param string $extraCondtion
* @return array $fieldnames
*/
function getAttributes($typeId = 1,$extraCondtion='')
{
    $resource = Mage::getSingleton('core/resource');
    $read = $resource->getConnection('core_read');
 
    /* eav attributes */
    $query = 'SELECT attribute_code FROM eav_attribute
              WHERE entity_type_id = ' . $typeId;
 
    $query .= $extraCondtion;
 
    $attributes = $read->fetchAll($query); 
 
    $fieldnames  = array();
 
    foreach ($attributes as $attribute)
    {
        $fieldnames[] = $attribute['attribute_code'];
    }
 
    return $fieldnames;
}

customer_import.php

<?php

$magentoFilename = '../../app/Mage.php';
require_once $magentoFilename;
 
umask(0);
 
Mage::app()->setCurrentStore(Mage_Core_Model_App::ADMIN_STORE_ID);
 
$customers = get_csv_to_array('customers.csv');
 
foreach ($customers as $customerInfo)
{
    $addresses = array_pop($customerInfo);
    $nzCustomerId  = array_pop($customerInfo);
 
    $customer = Mage::getModel("customer/customer");
 
    /// IMPORTANT : this localhost server only having store id 1 & website 1 SHOULD REMOVE THESE LINES or assign the correct store_id and website Id here
    $customerInfo['store_id'] = 1;
    $customerInfo['website_id'] = 1;
 
    $customer->setData($customerInfo);
 
    try
    {
        $customer->save();
        $customerId = $customer->getId();
    }
    catch (Exception $error)
    {
        Mage::log($error->getMessage(). ' :    ' . $nzCustomerId, null, 'customernotsaved.log');
 
        continue;
    }
 
    if($addresses)
    {
 
        $addressData = unserialize($addresses);
 
        foreach ($addressData as $address)
        {
                $is_default_billing = array_pop($address);
                $is_default_shipping = array_pop($address);
                $customAddress = Mage::getModel('customer/address');
                $customAddress->setData($address)
                        ->setCustomerId($customerId);
 
                if($is_default_billing ==1)
                {
                    $customAddress->setIsDefaultBilling(1)
                        ->setSaveInAddressBook('1');
                }
 
                if($is_default_shipping ==1)
                {
                    $customAddress->setIsDefaultShipping(1)
                        ->setSaveInAddressBook('1');
                }
 
                try
                {
                    $customAddress->save();
                }
                catch (Exception $error)
                {
                    Mage::log($error->getMessage(). ' :    ' . $nzCustomerId, null, 'customeraddressnotsaved.log');
                }
        }
    }
 
    Mage::log($nzCustomerId . ' => '. $customerId , null, 'customersaved.log');
 
}
 
function get_csv_to_array($file)
{
 
    $row = 0;
    $coloumnNames = array();
    $items = array();
 
    if (($handle = fopen($file, "r")) !== FALSE)
    {
        while (($data = fgetcsv($handle, 1000, ",")) !== FALSE)
        {
            $num = count($data);
 
            for ($c=0; $c < $num; $c++)
            {
                if($row ==0)
                {
                    $coloumnNames[] =  $data[$c];
                }
                else
                {
                    $rowData[$coloumnNames[$c]] =  $data[$c];
                }
 
            }
 
            if($row >0)
            {
                $items[] = $rowData;
            }
 
            $row++;
        }
 
        fclose($handle);
    }
 
    return $items;
}

This solution works pretty well to migrate customers from one installation to another (in my case 1.5 > 1.9).
With the standard import/export feature it is not possible to export many customers.

Solution was not created by me but was found here: http://anilpaul.com/magento-export-and-import-customer-from-one-server-to-another/