How would you go about manually writing a normal? Since it uses RGB, I would assume you would choose a color and use that. But how do you specify a specific color/normal in a surface shader?
The examples page actually should give you enough hints. If you want all vertices to use the same normal you can simply assign a vector to “o.Normal”. However i’m wondering why you need that? If you want the same normal for all vertices you usually simply change them in the mesh itself.