So what about your
Smart TV
Car
Washing machine
The list can go on , and sure you can get sometimes odd password turn up on internet but your talking about a"security" device
Simply put if the sub wants the eng code then he should know that you hold no responsibility for the system and nothing is warranteed you would have to be crazy to do it
If they already have code it's difficult to take it from them, but if you have contract of service to provide them , I wonder does it comply when you have a contract that sub has access to main settings?
Alarm monkeys? Does it matter to your efficacy insurance that you allow the sub to keep the engineer code ? Or I am looking at it the wrong way ?