Reducing the effectiveness of a safety feature

We just purchased a 2021 KIA eNIRO to use as our family car. As typical with EVs, this has to produce a fake engine noise to avoid squashing the hard of hearing (or animals) not expecting two tons of metal to be silently moving. When we test drove a 2020 car last year, there was a physical button on the dash to turn this off, on the premise that the noise sometimes isn’t required or appropriate, but it always defaulted to “on” for every start. As the car gets faster the noise also increases in volume, until after about 30km/h fading to nothing. In reverse the same thing happens with some additional beeps. Getting our 2021 car this year, the button was no longer present and the less-than-affectionately known VESS module cannot be muted. I can guess why, someone probably turned it off and squashed something or someone and someone in the UK/US/EU government understandably freaked out. KIA also removed the wire from the wiring loom, and won’t sell the 2020 button cluster, so it’s not even like you can retrofit a new car to act like the old one.

To be super clear: I don’t have a problem with the VESS noise, but because the “speaker” is in the front bumper the solution for going backwards is “turn up the volume”. Living in London means that houses are pretty close together and me reversing into the drive at 2mph shouldn’t submit the house opposite with a noise several times louder than a huge garbage truck. The solution in the various KIA owner forums seems to be “just unplug the VESS module” but this seems at best unethical and probably borderline illegal given it’s a device with the express purpose of trying to avoid hurting someone with your 2 ton lump of metal.

Given VESS is, as you might expect, just another device on the CAN bus and people have reverse engineered the command stream so you can actually just plug the VESS module into a USB device (with a CAN converter) and play with it yourself. My idea would be to make a modchip-like device that plugs into the VESS module using the existing plug, and basically MITM the CAN messages. All messages going from VESS back to the ECU get allow-listed (even though the ECU doesn’t seem to care if the VESS goes AWOL…) and any speed measurements going forward also get passed straight through. The clever part would be to MITM the speed when the “reverse gear” command has been issued, so that the car thinks it’s going about 20km/h backwards. This makes the VESS still make the engine and beeping noise but it’s only about as loud as the VESS module when going forwards when outside the car.

Technically this is quite easy, VESS->txrxCAN->MCU->txrxCAN->ECU and you can probably use an inexpensive Microchip reference board for a prototype. My question is more if this would:

1. Be ethical
2. Be legal
3. Invalidate my insurance
4. Invalidate the warranty of my nice new shiny car

Feedback very welcome!