I am actually fascinated by car electronics. I had heavily modified the software on mine, but it was easier than modern stuff, no encryption of the code, and even the checksum code only triggered a DTC with no consequences.
The only module that was encrypted was the main module, but it if you knew the security PIN you could do what you wanted. It was determined by people that if you observed the jitter of the CAN line fast enough, you could leak the pin via a side channel attack.
But modern car electronics are encrypted, and some probably have security processors that might trigger some irreversible states if you tamper with them. Modern cars are basically as locked up as a PS5.
P2 Volvo?
What changes have you made?