What is unreasonable, I suggest, is to expect your torture squad to be exposed to undue risk. One cannot insulate them from all risk because the job carries individual responsibility, like that of a surgeon or military commander, but it follows that once you are willing to countenance torture as a tolerated policy you must put in place the appropriate legal provisions and safeguards. I don't see the torturer being in a better position without laws in your example above. On the contrary, his position seems highly precarious as, perhaps, we are about to find out.
I am being only half-sarcastic as I do think focusing on the banalities of the logistics and legalities of such things as torture, or the holocaust or even the death penalty is one good way of throwing them into sharp relief. But, as a good functionary, I am also warming to the task. I suggest these classification:
A torture involving physical harm or pain
B torture involving psychological harm or torment
C other forms of lesser activity: practical jokes, shouting 'boo' loudly and unexpectedly, the comfy chair, waking the detainee in the middle of the night and telling him he has a phone call, pretending to shoot someone in the next room, or actually doing so (that might count as cat. B actually), secretly feeding him pork/bacon as the case may be, explaining there are no virgins etc etc
We don't need to be sidetracked by these details, interesting though they are. I still don't see why you won't countenance actual laws.