The issue of originality or not is a matter of individual choice. If you own the car you should be able to do whatever you like with it. It's your choice.
Whether it's advisable or not is an entirely different issue and thats a matter of personal taste.
I'm a hard liner on the matter of originality not because I don't think you should change your car but because it helps prevent fraud and misrepresentation where big dollars are involved. Over time what was wrong info originally becomes gospel later on because there is no longer any way to disprove it.
The problem arises when there is no yard stick to measure a car as a "genuine as it came from the factory original" if all the original examples have been modified to a greater or lesser extent.
This again is not a problem unless people knowingly or mistakenly claim the car to be original when it isn't. If a buyer isn't aware that what he/she is buying isn't what it purports to be then they are being defrauded either knowingly or not. This applies particularly to Cooper 'S' cars as there seem to be more "genuine original cars" about than were ever built by BMC.
There needs to be at least some genuine original cars about as well as people who can pick an imposter car. This requires not only people but a knowledge base of info. For Cooper cars Parnell's book is a start but it doesn't have a lot of info on Australian built cars and not all of it is correct. Unfortunately BMC Australia production info was dumped when the factory closed (or so folk lore says) so there is no factory info available for Australian produced cars. You have to comb through parts books etc to get info and even then it can be confusing, missing or simply wrong when compared to known genuine cars.
The list of model ID codes on this board is a start but it doesn't have all the necessary info such as internal production codes, engine and body numbers, car numbers and their likely ranges.
But does it really matter if you know what you have is or is not what it purports to be as long as you enjoy your Mini.
I'll get down from my soapbox now.
Regards
RonR