Magento 1.9 – Not Required VAT Field

You can achieve this with the following:

1. Copy app/design/frontend/base/default/template/checkout/onepage/billing.phtml and/or app/design/frontend/base/default/template/checkout/onepage/shipping.phtml to your template folder

2. add the check on the total value (subtotal, grand total,..) in the class attribute and change YOUR_TOTAL_AMOUNT to the total amount which you need as limit:

   <?php echo $this->getQuote()->getGrandTotal() >= YOUR_TOTAL_AMOUNT ? "required" : ""; ?>

The code of your input-form should look like this now:

<input type="text" 
 id="billing:vat_id"
 name="billing[vat_id]" 
 value="<?php echo $this->escapeHtml($this->getAddress()->getVatId()) ?>" 
 title="<?php echo $this->__('VAT Number') ?>" 
 class="input-text <?php echo $this->helper('customer/address')->getAttributeValidationClass('vat_id') ?> <?php echo $this->getQuote()->getGrandTotal() >= YOUR_TOTAL_AMOUNT ? "required" : ""; ?>" />

I didn't test it, but I think it should work #yolo.

According to http://zipcodes.guide-spain.com/Canary_Islands there are two postcode prefixes for the canaries, Las Palmas 35 & Santa Cruz de Tenerife 38. Assuming I've understood that correctly then:

In admin Sales/Tax/Manage Tax Zones & Rates you've probably got a tax rate for Spain setting it to your standard tax rate. Click add new tax rate call it something similar to the Spain one, but put 35* in the post code, and set the rate to zero. Do the same for 38*. You could also set the state/region here, but only if your store will require that in the address to select. Then in Sales/Tax/Manage Tax Rules you probably have a rule called something like standard vat which matches customer & product tax classes with tax rates. Edit it to add in your new tax rates in the multiselect.

You can test it in the basket using get a quote changing the post code to see when it adds/removes VAT