Are you asking if you can add an additional switch? If so, yes it's simple enough, though the wiring gets messy and with a switched light intended for hub dynamos and the light mounted in one of the usual places, it really isn't necessary. Maybe on some sort of cycle where you couldn't reach the light while riding it would be an advantage.
I added a switch when using a non switched light intended for a bottle dynamo with a hub, but the wiring annoyed me and I ended up going direct and it being on all the time, daytime lights before they were popular!