Magento: Update attributes source_model

update_attributes_source_model.php

<?php
require_once "app/Mage.php";
Mage::app();

$installer = new Mage_Eav_Model_Entity_Setup('core_setup');
$entityTypeId = $installer->getEntityTypeId('catalog_product');

// replace <my_attribute_code> with your attribute code
$idAttribute = $installer->getAttribute($entityTypeId, '<your_attribute_code_here>', 'attribute_id');
$installer->updateAttribute($entityTypeId, $idAttribute, array(
    'source_model' => 'yournewmodule/your_new_model'
));

// let's see if it worked
$attribute = Mage::getModel('eav/entity_attribute')->loadByCode('catalog_product', '<your_attribute_code_here>');
Zend_Debug::dump($attribute->getData());