How to enable / disable edit qty create invoice in magento

How to enable / disable edit qty create invoice in magento.

You can change enable/disable edit qty when create new invoice in magento.

Open you payment method model file.

Ex. You want to enable/disable edit qty when use "Cash On Delivery"

Open file:
/var/www/html/magentostore/app/code/core/Mage/Payment/Model/Method/Cashondelivery.php

class Mage_Payment_Model_Method_Cashondelivery extends Mage_Payment_Model_Method_Abstract
{
    /**
     * Payment method code
     *
     * @var string
     */
    protected $_code  = 'cashondelivery';
    protected $_canCapture = true;
    protected $_canCapturePartial = true;
    .....
    .....
    .....
}

Add  protected $_canCapturePartial = true; in this file.