Any thin electrical can be tampered. But you need to take more risk for doing this as digital odo's run with the help of an on board computer. If you dont tamper it the correct way, Then you endup with a malfunctioning computer which may inturn lead to a huge bill when you go for getting it replaced.
Yes the Digital Odo can be reset or tampered by connecting the Software to ECU and making changes.
I have read on some site that a person reduced the Reading by 2000kms of his BMW which was leased. He did tampering since the car had crossed 2000kms more than that required for Service Interval.
Reversing the modern so called digital ODOs is easiest of all, it just requires a bit costly equipment to do so. Put the car in limp mode (not all cars have this feature, also, manually putting the car in limp mode is tricky and requires knowledge of sensors, easiest is to manipulate the O2 sensor), put the car in reverse, and turn on the ignition to ACC. Now, the actual device comes to picture. It's a small palm sized remote with a wire to attach to the ECU. It has a few buttons apart from the magical LOOP button (not sure why it is so called). Just press this button and VIOLA, you'l see the odo moving backwards at the speed of light. Have personally seen this but have no pics of the process.