Hi,

You could set default value of "Display in navigation" for specific page type in Admin mode

Go to:  Admin mode->Content Type->[Page type from list]->Default values    and unclick two checkboxes:

- Use adjusted default settings for pages using this page type

- Display in navigation

You can also override the SetDefaultValues method in your ContentType class.

public override void SetDefaultValues(EPiServer.DataAbstraction.ContentType contentType)
{
    base.SetDefaultValues(contentType);
    this.VisibleInMenu = false;
}

Thanks for your answers, both solutions worked as expected.