If we screw up that wordpress url when we need to go into the database and change it back, right?
That's one way. Another is to use update_option() in your theme's functions.php file.
http://codex.wordpress.org/Changing_The_Site_URL#Edit_functions.php
Are our absolute links going to break
If you're also moving content as well then the absolute URLs in that content will break. So you need to (safely) search and replace the old references from http://www.sitename to http://www2.sitename within the database.
See this article for more info.