Can you cite the law? I know the EPA has civilly pursues companies that make products that bypass emission controls. But haven’t seen or heard anything that goes as fat as you suggest.
E.g.: https://www.dinancars.com/products/software-tuning/engine-tu...
This allows you to change the engine programming on a BMW. They do note it is not legal in California.
Tampering. You may not remove or render inoperative any device or element of design installed on or in engines/equipment in compliance with the regulations prior to its sale and delivery to the ultimate purchaser.
https://www.ecfr.gov/current/title-40/part-1068/section-1068...
It seems primarily about bypassing or disabling emission controls, not user controlled fuel mapping, or mods like putting in a performance air filter or exhaust. But EPA does consider a flex fuel conversion tampering.
https://afdc.energy.gov/bulletins/technology_bulletin_0807.h...
With a relevant paragraph on page 2
The site you linked mentions the carve out that the EPA has, but note that it requires both retaining or beating original behavior and requires extensive prod of that fact. A similar law affecting phone home circuits would almost certainly not find disabling the ability to phone home as in compliance.
They just got a $10M civil judgement against a couple "diesel tuners" here in Michigan:
https://www.justice.gov/opa/pr/united-states-awards-10-milli...
https://www.epa.gov/enforcement/national-enforcement-and-com...
but yeah, this is civil action against vendors, not anything that police will fine people for on the side of the road.
Laws against tampering with vehicle safety devices would easily have a similar effect on your built in phone home systems.