if you use NSU it logs your device and what firmware you have on it, how many times you've updated your device and with what versions etc, so they know you've been changing firmware just by putting your imei number in the computer at the care centre.
not sure how it works with the other flashing tool as i've not used any.
changing product code on s60 to get different firmware versions invalidates your warranty, if they decide to do a check when you send it for repair and repair guy is a tosser, but sometimes they dont care its like a lotto but not worth the gamble.
so i'd expect them to go with same policy across all there devices