How do you modify the web.config appSettings at runtime?

Question

I am confused on how to modify the web.config appSettings values at runtime. For example, I have this appSettings section:

Answer 1

And if you want to avoid the restart of the application, you can move out the appSettings section:

to a separate file. And in combination with ConfigurationSaveMode.Minimal

var config = System.Web.Configuration.WebConfigurationManager.OpenWebConfiguration("~");
config.Save(ConfigurationSaveMode.Minimal);

you can continue to use the appSettings section as the store for various settings without causing application restarts and without the need to use a file with a different format than the normal appSettings section.