There's no kill switch. The F35 advantage is the mission data files that are frequently updated and allow the F35 to classify targets and threats. Essentially the US and partners collect the electronic signatures of enemy radars and package them so in a conflict the het can draw a box with a S400 label.
So it doesn't have a kill switch, it just stops being useful when it can no longer regularly phone home? That sounds awfully close to a killswitch to me...
Countries could generate their own MDFs but what's the point, it's from shared intelligence. Which is the premise of an alliance.
Sometimes variances in manufacture or maintenance of electronic systems allow the F35 to identify not just type of system but exact unit.