Posted on May 09, 2011 | Magento 1
In order to set these defaults, you need to modify the opcheckout.js file located at:
frontend/base/default/js/opcheckout.js
Add this code to the end of the initialize function:
initialize: function(accordion, urls){
...
// Set guest checkout by default
if ($('login:guest')) $('login:guest').checked=true;
// Set shipping = billing by default
if ($('billing:use_for_shipping_yes')) $('billing:use_for_shipping_yes').checked=true;
},