but even so, the chances of accidently setting off the alarms are exceptionally remote.
Aircraft in the FIR squawking 7000, gets an airborne IFR clearance with the squawk 7701 (yes, it can happen). Dials in second '7', gets distracted, doesn't do final '1' quick enough.
The alarms will go off.
Now, having said that, there's no reason why you shouldn't leave it on when you're changing squawk. With new transponders you just push-button the code in anyway. However, be careful when you're doing it for the above reason.