This is not possible. The urls file isn't read each time a request comes in. It runs when you start up an instance of django before requests are being handled.
The suggestion made by user995394 would be the way I would handle it.
Digging a bit deeper if you did want to do this. You could specify a request middleware.
class FooMiddleware(object):
def process_request(self, request):
if request.user.is_authenticated():
request.urlconf = 'myproject.authed_urls2'
I tested the above middleware in a django project. When I login the alternate file is handled for that request while in another window a non authenticated user is still using the original url conf.
Still though, I recommend using decorators on your views. If you are concerned with people discovering urls that only staff should know about you can have your auth required decorator respond with NotFound
instead of NotAuthorized