Here's a short version of a long story.
I am running two instances of WP on the same machine. mysite.org/ and mysite.org/newsite. My eventual goal is to move /newsite to /.
1. While finishing up building /newsite, I accidentally changed the WordPress URL on the General Settings page on /newsite to /newsite/blog, which totally messed up the site I was working on.
2. I found this page, which instructed me to hard-code the correct URL into wp-config.php (http://codex.wordpress.org/Changing_The_Site_URL)
3. I did that, and now both / and /newsite work fine. (I don't want to embarrass the site by giving you a URL, but trust me that it's working.)
4. My eventual goal is to move mysite.org/newsite to mysite.org without totally messing up the site again. Can someone please advise me how to un-hard-code wp-config.php and how to move the site?