If you fudge up you wordpress installation to the point where it is not even accessible this might be a way to fix it.
Log on to the server hosting your database (or do it remote via mysql) and do a dump of the database in question with mysqldump:
bloghost# mysqldump -p --databases wordpress >> wordpress.sql
Then open your file in an editor and browse to the setting that is causing the trouble and edit it back to normal!
Then it is just to import the database back into mysql with mysqlimport or to simply pull it in via the mysql command like this:
bloghost# mysql -u user -pyourpassword < wordpress.sql
And you are good to go again!
The good thing about wordpress is that it stores this enormous amount of stuff in the database and not just the posts. And as a bonus, since the site was unavailable you know that the info you wrote back into the db is the latest and nothing got lost on the way!
However, there are plenty of opportunities to make more damage than good this way, so do not blame me if you brake anything taking my tip. If you do, you probably should not have been there anyway!