Then I suggest you get a local installer to do the battery change.
The master user certainly can place the system in service mode, enter code, activities, advanced settings, service mode.
You should be able to change your batteries, if the system when you exit the service is causing tampers, unset the system, go do a walk test and that should clear it.
I believe that its only an issue if any of the detectors are 1 way ones, and as the Agility 3 has a 1 way and a 2way range of devices and I have no idea what you have this is the easiest way to make sure you have few issues after changing the batteries.
Secondly you should in any case you should always check any device you have done anything with, as how do you know its still working after you have played around with it ????