Hi David, there are no examples or documentation I'm aware of. But I can give you a sample.

namespace <Company>.DDRMenuProvider
{
using DotNetNuke.Entities.Portals;
using DotNetNuke.Web.DDRMenu;

using MenuNode = DotNetNuke.Web.DDRMenu.MenuNode;

public class MyModule : INodeManipulator
{
public List<MenuNode> ManipulateNodes(List<MenuNode> ddrNodes, PortalSettings portalSettings)
{
ddrNodes.Clear(); // Removes all nodes present (by default DotNetNuke Tabs)
ddrNodes.Add(new MenuNode { Text = "YourText", Url = "YourUrl", Parent = parentNodeIfAny }); // Or any other properties, note some like First/Last etc are automatic

return ddrNodes;
}
}
}

Once you compile it you need to pass type of this manipulator to DDR. If you have it as module on page, go to its settings and set Node Manipulator type to "<Company>.DDRMenuProvider.MyModule, <Company>.DDRMenuProvider" (without quotes, first is path to class and second is assembly name). You can pick any namespace you want. Let me know if it works for you.

Yes if you omit ddrNodes.Clear() you'll have DNN Tabs in navigation, I included it in case you want to create new navigation instead of modifying existing.

You set this manipulator on instance of DDRMenu you wish to be manipulated. It can be module, skinobject or code instance.

1. After you place DDR Menu module on page you go into its settings.
2. For SkinObject you set it inside your skin like <dnn:menu menustyle="MegaMenu" NodeManipulator="<Company>.DDRMenuProvider.MyModule, <Company>.DDRMenuProvider" runat="server"></dnn:menu>
3. For code instance there should be NodeManipulator string property.

I don't think you can set this manipulator to affect all DDR Menus globaly if thats what you want. You need to specify it for each instance manually.