Again, the letter i'm referring to was from HKMC, not the bank, and I suggest yours was too.
This has implications for the perceived risk being discussed: You need to remember that the purchase I'm taking about was in 2009 - Long before the special buyer stamp duty came in. So then, the only mechanism to check that you were occupant, was that solitary letter.
Clearly the purpose of this check was to ensure that the HKMC wasn't giving low interest top up mortgages to landlords speculating on ever increasing prices, and yet they still only sent 1 letter, and never had ANY interaction with the owner otherwise. They trusted the bank completely to guard this mechanism.
The bank for their part has never sent ANY letters to check on occupancy, zero, nada and so that shouts loud and clear that both the HKMC and the bank simply didn't care much. Born out entirely by real world examples.
Fast forward to post SSD (special stamp duty) and buyers of multiple properties now have to stump up 20% extra - There are far more checks and legal hoops to jump through to satisfy that criteria, so why still bother with the flipping letter? - Because it's legacy from their old way of doing things.
Read between the lines and you'll see that really the HKMC don't care if you rent out your property, what they care about is not financing people to own more than one property and building a rental business out of it that makes property unaffordable for people simply seeking to buy and live in a home. Which is the EXACT objective of the HKMC - to make property accessible for joe average. Does the ability to rent out your home if your circumstances change decrease or increase the accessibility of property to joe average?
If no one is trying to catch you making a minor infraction of the rules that they don't really care about anymore, you chance of getting caught is much much lower than many posts on this thread would suggest.