No, it would be much different. Go to the Studio->Designer->Injections->Head injection area and place there the following code:

<script language="javascript">

$(document).ready(function() {

  var oField = $(".bx-form-input-location-country");

$.each(['GB', 'CA', 'US'], function( iIndex, sValue ) {

   oField.find("option[value='" + sValue + "']").val("---" + sValue);

  });

  oField.find("option:not([value^='---'])").remove();

  oField.find("option").each(function(){

   var sNew = $(this).val();

   $(this).val(sNew.replace('---', ''));

  });

});

</script>