Modify application settings in .NET 2.0

(Settings1.Settings) you can't change application settings in code. You can only change user
settings. To change the application settings, you need to write your
own code to open the configuration file as any xml file and modify it

http://blogs.msdn.com/mohamed_sharafs_blog/archive/2006/12/12/using-application-user-settings-in-c-2-0.aspx