The USPS Shipping server behave is on the confirm_cart.php page.
open that page, and open the server behavior panel, then double click the USPS Shipping server behavior to edit it and change the user ID.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.