@yesaul, I chose to make a slightly different change so that the corrected validation would apply to both the admin and the storefront, changing /includes/classes/VatValidation.php:
Code:
    // -----
    // The class constructor gathers the to-be-verified country-code (2-character ISO) and
    // the associated VAT Number.  The "VAT Number" value must include any country code
    // prefix.
    //
    // Since we'll need the SOAP service to automatically validate the VAT Number, check now
    // to see that the PHP installation includes that service, logging a warning if not.
    //
    public function __construct($countryCode, $vatNumber) 
    {
        if (defined('VAT4EU_ENABLED') && VAT4EU_ENABLED == 'true') {
            $this->debug = (defined('VAT4EU_DEBUG') && VAT4EU_DEBUG == 'true');
            
            // -----
            // Greek VAT numbers start with 'EL' instead of their country-code ('GR').
            //
            $this->countryCode = ($countryCode == 'GR') ? 'EL' : $countryCode;
            $this->vatNumber = strtoupper($vatNumber);
            
            if (!class_exists('SoapClient')) {
                trigger_error('VAT Number validation not possible, "SoapClient" class is not available.', E_USER_WARNING);;
            } else {
                $this->soapInstalled = true;
                try {
                    $this->_client = new SoapClient(self::WSDL, array('trace' => true) );
                } catch(Exception $e) {
                    $this->soapInstalled = false;
                    trigger_error("VAT Number validation not possible, VAT Translation Error: " . $e->getMessage(), E_USER_WARNING);
                }
            }
            $this->trace("__construct($countryCode, $vatNumber)");
        }
    }