With your permission, I will re-post the code including your idea. The changes are simple to make:

Add the abstract keyword to the appsettings declaration as shown below:

public abstract class appSettings
{
…
}

Make one change in the Load Method (which are only necessary due to an oversight on my part origianlly:

In the load (lines 119-120) method change:

appSettings appSet = new appSettings();
XmlSerializer xs = new XmlSerializer(appSet.GetType());

to this:

appSettings appSet;
XmlSerializer xs = new XmlSerializer(this.GetType());

Finally, create a class declaration similar to the one you proposed in your comment in your application.

And you are good to go. I tested this implementaion and it works fine and includes your new public settings.

Thanks again for pointing this out.
G

Then,

public class MyAppSettings : AppSettingsBase {
public int myappSetting1;
public string myappSetting1;
}