That's not the order it works in.
The checkout flow is: Shopping Cart->Shipping Address (and method selection)->Billing Address (and payment selection)->Confirmation.
If one wants to change an address, they click on the Edit Address button, which takes them to the appropriate page to do that, and that page sends them back when done.

You seem to be talking about validating shipping addresses, but now you're talking about validating billing addresses, and then going back to shipping.
If your customization requires the insertion of another page in order to work, make sure you're not actually adding a lot more to the checkout process, since the more you complicate it, the more you'll find customers abandoning your site in favor of a site that's less confusing.

Most people are asking for ways to *shorten* the checkout process, not ways to *lengthen* it by adding more pages/steps.

As explained earlier, I recommend that you do your validation as part of existing pages, instead of adding more pages.