If I have in the web.config file of web application :
<appSettings>
    <add key="DD" value="567_Access"/>
    <add key="ValidationSettings:UnobtrusiveValidationMode" value="None"/>
</appSettings>
I know how to read the data in appSettings sections like this :
 string accessD = ConfigurationManager.AppSettings["DD"];
But I want to know how to Modify (Set) the value of a key in appSettings
Through the code ?
(I want through a specific check to this value to stop the application under some circumstances)