It is also likely that similar code modifications need to be made to files relative to customers UPDATING existing address entries in their "My Account" area.

We think that only one file needs looking at here:
tpl_modules_address_book_details.php

... where similar addition of jscript and line modifications to various input fields' PHP need to be made.

Again... the intention is to make sure that whatever a customer enters (whether at Sign-Up, or Address Editing later on), the postcode will at least be upper-case.