As I mentioned originally, you can't add the exact same instance of a node to the scene tree multiple times. If you need multiple KB2D nodes in the scene, you'll need to create each of them as a separate instance.
That said, you can do that via code.
You could create a separate scene that contains the KB2D itself (and anything else you want to part of the scene). Then, you could create instances of that by
preload()ing the scene, creating copies as necessary via the
instance() function, and then adding them to the scene via
Or, you could create new KB2D's from scratch in code via:
var new_kb = KinematicBody2D.new()
Then, you can set whatever properties you want on the new kb, and then finally add that to the scene via
Either way will work. Using the first method, you're creating instances of a scene that you created ahead of time. Using the second method, you're creating a brand new KB2D from scratch and setting it up completely in code.