There are places that do 'clock corrections', 'kilometer-corrections', or 'mileage correction'. For whatever reason people need the motorcycle-clocks changing on digital speedos, these places are mostly located in the neighborhood behind MBK (Mah Boon Krong) center in Bangkok.
It is remarkable that this district of Bangkok was one famous to foreigners to unlock SIM locked mobile phones, now they apparently upgraded and can turn back any digital speedos of motorcycles and cars.
Some of this shops do provide by courier services, you send them and they send back, some shop say they daily receive up to 20 clocks a day for alteration. It is not against the law in Thailand, and therefore this business is blooming. Recently I met a guy who was from Germany, traveling Thailand as holiday destination “I come often to Thailand, I let them turn back then clocks for my bikes for a few Euro's and back home the value of my bike is going up by 100s of Euro's”