I suppose it’s possible to create a script or plugin that would monitor the WP settings URLs in Dashboard >> Settings >> General and do a global change when needed, but such a script would be complex ad fraught with issues when handling the different img and a href links in post/page content, as well as in all the tables – plain text and serialized – in the database.
It’s not difficult or time consuming to change the site URLs the usual way. The best references are the WP docs at http://codex.wordpress.org/Moving_WordPress
When Your Domain Name or URLs Change
When your domain name or URLs change – i.e. from http://example.com/blog to http://example.com, or http://example.com to http://example.net – there are
additional concerns. The files and database can be moved, however
references to the old domain name or location will remain in the
database, and that can cause issues with links or theme display.If you do a search and replace on your entire database to change the
URLs, you can cause issues with data serialization, due to the
fact that some themes and widgets store values with the length of your
URL marked. When this changes, things break. To avoid that
serialization issue, you have two options:1) Only perform a search and replace on the
wp_posts table.2) Use the https://interconnectit.com/products/search-and-replace-for-wordpress-databases/ Search
and Replace for WordPress Databases Script to safely change all
instances.
Or search for various plugins that do much of the work for you: http://wordpress.org/plugins/ There are several to choose from, including premium (paid) plugins via a Google search.