How can I change (or override) a settings.settings variable by adding a variable to the app.config on production?
Is this possible anyway?
Only through code:
e.g.
if (bool.Parse(ConfigurationManager.AppSettings["overridethis"].ToString()))
{
//use overridden value
}
If however, your issue is maintaining different configuration values in different environments, then I would use AppSettings instead.
You can then use a developer override file.
See http://www.compiledthoughts.com/2005/03/overriding-webconfig-app-settings-with.html