It would cost a fortune to do that with no real benefit; you want this cable in the hands of someone you presumable know and want to target. Scary!
For activists in dangerous places, like, say, Russia or Iran or Hong Kong, yeah, it could be pretty scary. Like life & death scary. But I agree there's virtually no way to protect against it, since government agencies who really wanted you could just intercept an internet purchase while in the heads of the delivery company and switch them there.