they have every right to refuse your grey imported car which some dealers may exercise
and what do you mean by general maintenance anyway, oil change? when they dont even have the original oil and air filters for your car and engine codes are different why would they even entertain an oil change or sparkplugs, they could refuse IF they wanted to so that later you cant claim that anything got messed up. similarly transmission is completely different it takes a different oil than regular hrv , the whole power train, software, ecu is different, its common for any 3S to refuse to service a grey import car as they dont know what problems maybe lurking with it which they dont have the ability to fix.
again depends on that particular dealer, try another honda 3s, like mentioned above some honda and toyota dealers do service grey imports as well byt they have the right to not entertain as well.