The OBD port can easily spit out a read only mileage reading which is not tampering with the recorded value in the ECU. The OBD port is supposed to be user accessible and usable by the end user and 3rd parties (at least in the EU) even though manufacturers are trying their hardest to put “non diagnostic data” behind their proprietary software and/or wireless comms. Reading the data from the OBD port isn’t (at least shouldn’t) be classed as tampering.
One of the ways tampering happens on digital dashes that read the mileage from the ECU is by putting a interceptor in between the dash and the ECU as it’s easier than reprogramming the ECU. https://youtu.be/f4af1OBU5nQ