Question of curiosity:

Is it possible to add additional division/unit patches for selection at the pilot creation screen on Longbow 2?

Possibly, have you explored the file structure or some of the modding tools?

Yes, it is possible. I've already tried this.

Simply make the image around the same size and the same properties as the existing ones and place it in the '.../PData' folder. It will then be available in the pilot roster screen.