Nah, just go ahead and do it. Cars pass ADR's during manufacture. If the head lights came off a Australian sold car then they have passed ADR's. Been through all that crap just recently with an AC Cobra. Everything fitted to it must come from another Australian car ie. engine, door locks, all external lighting, seats, seatbelts etc. Anything not off another car must be engineered ie chassis etc. I guarantee you'll be fine. Do it neat, like you would your own car anyway, and no one will care. Not Vic Roads nor an engineer. It's not strucural. At least you asked before cutting though.