It didn't work.
Actually, the only field I can't change is "Appearance". The rest of the list:
3-D Secure Transaction, Company, Contact Us Form, Email, Email Notifications, General, Logging, Product Search, SEO, Security, Shipping, User Profiles
Can be changed. And (I think) they are all accessed from the same file "configuration.php".
That's why I really don't get where the problem is...