There needs to be a physical "OFF" switch for the wireless connectivity, too.
It's possible I could compromise on wi-fi or bluetooth, because those need to be paired to communicate. Hard no to cellular of any kind, if for no other reason than it means that the car's location is being continuously tracked and logged for all time by the carriers and national military.
I hate it for the fact alone that it enables location tracking via cellular connectivity as I assume that the SIM is connected all the time.
I'm willing to bet there are militaries and state intel agencies in the EU that have obtained brand new passenger cars that don't have transceivers in them. The module is also probably fairly easy to physically rip out, too, without disabling the whole vehicle, if creative methods with more finesse don't pan out.
Does nobody at all in governments see what an existential danger it is to a free society for anyone in that society to have access to a database containing the complete transportation logs of every single member of the society? I can't be the only person who sees this is an existential threat to a small-l liberal democracy; there are people alive in the EU today who suffered under the USSR and DDR.
I'd be worried even if it were a benevolent person with these logs; I'm positively terrified knowing it is the phone company and their pals in military intelligence.
Maybe. But does anybody in the governments think that the free society withering away is the danger to the government? Perhaps during the Cold War they thought so, but nowadays...
It's a legal requirement to have it. Sure, I can rip out the head-lights too, but then I am not allowed to use the car any longer on public roads. If emergency call is part of the cars registration I am probably not allowed to disable it without voiding the registration.
As well, no one does this. If you do it, you stand out like a sore thumb.
It's internal to the vehicle, so I doubt it would stand out visually. The ALPR stuff and mobile towers aren't (yet) integrated.
I can't do that for a GSM radio built into my car if my car has to be on to drive from A to B.
This was 15 years ago: https://en.wikipedia.org/wiki/Data_Retention_Directive
Sure, it eventually got struck down by the courts, but EU politicians still thought this was a terrific idea. And it's not like things have changed much since then.
(I was looking for my "smart" TV, I ended up disconnecting the wireless card from the TV. Thankfully the error message isn't as annoying as other models.)
There's no real standard for cellular antennas as there is for many other types of radios (as far as I know, not that I would / can find in some brief looking). Most stuff I'm familiar is 50ohm or 75ohm. E.g., wifi antennas are generally 50ohm. If you made me pick a resistor to put on there without being able to test anything first, I'd pick a 50ohm/5W. But you might burn your electronics up.
So your two main unknowns are the impedance and wattage.
Solving for wattage is probably best just done with Google. The power output should be fairly standardized. Assume the transmitter's going to go into its highest power mode when it realizes it can't find anyone to talk to and then leave yourself some headroom on top of that. On a very brief look, most sources put LTE at about a half a watt, but other techs at up to 3-4W. For the price of resistors and assuming these will end up mounted somewhere without great airflow, I'd probably just throw two 5W resistors at it.
Solving for impedance is going to be a bit more challenging. If you're lucky, an off-the-shelf antenna _may_ be marked with the frequency ranges and impedance. Otherwise, measuring impedance generally requires some more specialized tools. You could pick up something like the NanoVNA2 to do the measurements yourself (they're not the best, but likely close enough for what you're doing and cheap relative to the other options), or try getting in touch with your local ham radio group and ask if anyone has an antenna analyzer to analyze a cellular antenna (impedance is at a given frequency, so they need an analyzer that covers up to at least around the 1GHz range, which are less common than one for HF which is only covering up to a few dozen MHz) and could analyze an antenna for you.
Then just hop on Digikey/Mouser/etc, grab some resistors and a SMA or whatever other connector would plug in in place of the antenna and get to soldering.
Disclaimer: Amateur radio guy, not RF engineer. It's been years since I actually used any of this information in any significant way. This could all be entirely wrong.