I suspect that's not far off from what Israel did, from my understanding they modified a device's at a production level, it sounds like they essentially redesigned the pager.
It will be interesting to see how they did it with the radios.
I feel like a broken record reminding people that the TAO (Tailored Access Operations, now Computer Network Operations), part of the NSA, has been doing this for 20 years. Except they implant spyware instead of explosives. Probably.
They blew up a Soviet pipeline by leaking bad pipeline turbine designs via the Line X program. Nothing to do with the NSA hacking supply chains and more due to double agents leaking deliberately bad designs, and the Soviets failing to stress test them.
The NSA was created in the 50s and was around at this point; this was the CIAs show.
You could get a new battery from a known good source (or light a couple on fire to make sure they're not explosive). It should be relatively easy to check the rest of the components for anything near a dangerous amount of explosive, and the body can be replaced with a custom one and/or subjected to the fire test.
Even a fire test may not produce accurate results (see C4). Better to not have distinct supply lines from the civilian population you're already hiding in.