It is a mystery as yet and it is one i would like to know my self, i answered a bit in haste last night but this is what i have learnt so far about it. Dji claim they are factory set according to there shipping destination, i have emailed them a number of times about this and have had the same reply every time, but we all know we cant take this as solid. The next is a company in the uk were selling the pros cheap on ebay a few months ago for £899, i contacted dji about the company to see if they were legit and knew of company as they seemed far to cheap. Dji replied that they were one of there american distributors somehow selling them in the uk cheap on ebay and must have got round import and tax somehow. They told me that these carfts would be FCC models and if flown in the UK it would be against EU regulations and i would be breaking the law. I contacted quadcopters.uk and heliguy and they both confirmed that they knew of this seller in the uk selling them cheap on ebay and that they were FCC models and against the law to fly in the uk. So after all this a few months ago i was pretty convinced they were factory set according to there shipping destination.
The other week there was a thread on here with someone believing it could be something to do with the App we use and our tablets which might set it which is an interesting though.
I do wish someone would hack this tho and find a way round it, if nothing else but to learn the truth about how it is set, one thing for sure is dji do not want us finding out about this, maybe that's why they say they are factory set, to throw us a curve ball maybe.