As far as I know, you have to add them by hand. Off the top of my head, here are the things to do:
Open up two editor windows, one for your new Austria mod and one for the Napoleon scenario(Or any scenario with Austria in it).
Add the civ, filling in all the blanks with whatever is in the Napoleon civ, or changing what you want.
Add the Hussar unit. I think it is supposed to be 7-3-3 with a cost of 80.
Cut and paste the civilopedia entry for the civ and the UU from the Napoleonic scenario folder into the civilopedia in your Austria mod.
Add the Pediaicons for the civ and the UU(Hussar).
Add the leaderhead flc's.
Add the civ in 'Scenario Properties' screen in the editor.
I think that's all you have to do.