Runtime Editing Web.config App.config

You can Edit web.config and app.config file on run time also.
Web.config configuration files & app.config project item files, which get converted to "ExecutableName.exe.config" at build time, both support the convenient appSettings section with its own read method in the System.Configuration.ConfigurationSettngs class. The appSettings section stores element name / value pairs in the format:

<add key="elementName" value="elementValue" />..... more