Criteria used to determine if a "Chinese inch" is an "inch"?

I can't determine if the compound "Chinese inch" is endocentric in that the sense of "unit of length" is preserved, or if it is exocentric since the length is indeed appreciably different in the same manner that a "kilometer" differs from a "mile."

I would say it is definitely endocentric, as the compound still has "inch" as its head. The meaning of "measure of length" is not essentially changed, as is the case with fluid ounce and light year.

Inch was never by any standard a fixed length, even though we tend to see it that way nowadays. The inch is traditionally equivalent to the thumb (Dutch duim, French pouce), even today in French, an inch is called a thumb (pouce). Just like the yard, which seems linked to the old ell or cubit (Dutch el, all related to the length of the arm between elbow and the top of one of the fingers), or the foot, it had a common definition, but since humans are all built differently, its actual size would basically depend on the person measuring.

Standardization set in at some point, but even then, there have been (and in some cases there still are) different standards between countries or even inside countries.

In that perspective, it is not strange to see "Chinese inch" as just another standard length, in this case a Chinese standard, just like the similar compounds imperial pint or nautical mile.

As for your concerns about the risks of mixing up or misinterpreting different standards of measurements, those concerns are valid, and have existed throughout human history. That is the reason that for as long as we can trace back, people have tried to standardize measures, whether they were measuring amounts of grain, distances or weight of gold. And after thousands of years of these efforts, we have still not managed to truly implement one working standard, as is illustrated by the crashing Mars probe - and even closer to home, people in "metric" countries still buying and selling pints of beer and pounds of meat without seeming very concerned about any official and strict definitions of those measures (for most, half a litre and half a kilo for the pint and pound respectively are good enough).

A Chinese inch is simply a unit of measurement. It has no relationship to the inch, it's just called that way in English. No, inches are not a class of unit, an inch is an inch but a Chinese inch is something different.

There are many examples of such qualified names for units of measurement. For instance, the American pint is 473 ml while the British pint is 568 ml. A billion means 10⁹ in the US but 10¹² in the UK. It's not that they're both members of the class millions, or pints, they simply mean different things in the different dialects.

The Chinese inch is the name adopted in the English language for the Chinese cùn. It is not one of many inches, it is the Chinese inch. So no, no semantic change has occurred, the Chinese inch is to an inch as a kilometer is to a mile.