I remember in the late 70's early 80's, odometer readings wound back were an issue, but as you say not much today; Many NZ's particularly younger 18 - 25 don't tend to keep cars that long anyway as compared to about 20 - 30 years ago. I have bought many cheaper/older cars (1992 - 1996, > 150, 000 k's), to repair for resale, and generally engines are still pretty intact with good compression.
Often the odd suspension part/cv joint, air flow meter, power steering reservoir are worn/non functioning. Engine manufacturing tolerances have become better I believe, and after 30 years of repairing cars/engines, it has become much less frequent (Though bit more difficult - mainly due to limited engine bay space) for Asian cars made after about 1990...
I personally have never heard it was possible to reprogram the odometer. But nowadays, I think LTNZ requires imported cars (by dealers) to have a history service record (ie. in Japan, factory scheduled maintenance intervals with recorded odometer readings). Really, it's not as easy as it use to be to cheat the #s.Bit of a myth I'm afraid. It turns our that with the right equipment it is much easier to roll back a digital odometer.
It is possible. I know of a motorcycle crash that requires an instrument cluster replacement and when a brand new cluster was installed (hence brand new odometer) the owner requested for the odometer to read the same to the old one, and it was done with no questions asked (although the owner did explain his case to the garage).
edit: it's the digital odometer I was referring to.