App.Config file help

<configuration>
    <appsettings>
      <add key="DatabasePath" value="Database=C:\Users\Roelof\Documents\Visual Studio 2008\Projects\ClientServices <br mode=" hold=" />        \Database Information\Database\\CLIENTSERVICES.FDB;User=SYSDBA;Password=masterkey;Dialect=3;Server=localhost" />
      <add key="RegisteredHDD" value="No" />
      <add key="Activationcode" value="" />
    </appsettings>
</configuration>

System.Configuration.Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
                    config.AppSettings.Settings["RegisteredHDD"].Value = "Yes";
                    config.AppSettings.Settings["Activationcode"].Value = final;
                    config.AppSettings.Settings.Add("LastDateFeesChecked", DateTime.Now.ToShortDateString());

                    config.Save(ConfigurationSaveMode.Modified);