I disagree with your notion that cars are not tempered in Japan before shipping. I can give you a living example out of my own experience when I was importing a car for my personal use from Japan. I had the option of going with either an Australian, Canadian, Srilankan or Pakistani middleman sitting in Japan to bid on the vehicle for me for export to Pakistan.
Both Canadian and Australian out rightly refused to tamper the meter for me, however, on reaching out to the Pakistani and Srilankan exporters both agreed to do provide the meter roll back service for 10,000 Yen and 12500 Yen respectively.
And it has nothing to do with export certificate as cars are not reinspected after the certificate has been issued. So, this can be done prior to shipping the vehicle out of Japan if the exporter doesn't wish to abide by the law of the land.
Having said that I agree that a lot of the local dealers in Pakistan have this done once the cars reach Pakistan. It's a personal choice made by dealers, but meter roll backs can be done both in Japan before shipping the vehicle, and once the car reaches here.
It's less risky to do in Pakistan, hence a lot of dealers go with the idea of doing this here simply because of virtually no law to control this menace here. Whereas in Japan, if reported to the local authorities your car association membership can be cancelled and you can be blacklisted. However, there are still a lot of Pakistani, Indian, Bangladeshi, Nigerian, Srilankan, Ugandan exporters in Japan who are willing to take the risk to provide this service.
No point for guessing why I went with the Australian exporter. It was a trouble free import thankfully.