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Reordenar o adicional tooltip a campos del billing address
http://inchoo.net/magento-2/frontend/reorder-input-fields-shipping-billing-step-magento-2/

  Dentro del di.xml crear un plugin como este
  
  <type name="\Magento\Checkout\Block\Checkout\LayoutProcessor">
        <plugin name="checckout-billing-fields-personalize" type="\Daytours\Checkout\Plugin\Block\Checkout\LayoutProcessor" sortOrder="1" />
    </type>
    
    
    Para el observer 
    
    //        $jsLayoutResult['components']['checkout']['children']['steps']['children']
//        ['billing-step']['children']['payment']['children']
//        ['payments-list']['children']['checkmo-form']['children']
//        ['form-fields']['children']['postcode']['sortOrder'] = 71;

//        $jsLayoutResult['components']['checkout']['children']['steps']['children']
//        ['billing-step']['children']['payment']['children']
//        ['payments-list']['children']['checkmo-form']['children']
//        ['form-fields']['children']['country_id']['sortOrder'] = 0;

        $jsLayoutResult['components']['checkout']['children']['steps']['children']
        ['billing-step']['children']['payment']['children']
        ['payments-list']['children']['checkmo-form']['children']
        ['form-fields']['children']['country_id']['tooltip']['description'] = 'asdasdadads ad dad as';