To be honest Graham, and as others have said, uprated brakes to discs, maybe some nice adjustable front seats, a 5 speed box, possibly uprated front and rear shocks and, say, a 1275 engine is by no means 'too revolutionary' lots of people have done it already and that is what i'm going to do with my car.
Some would argue that this sort of improvement is what the Minor should have had after the 1964 upgrade so, if you are intending to do this to your car, it will not in any way affect its DVLA classification, appeal or status. indeed, unless you knew, the car would probably look exactly as it does now with all the improvements hidden from general view.
There are lots of threads on the original v modified debate and you can amuse yourself reading all the various views but, at the end of the day - it's your car. If it is going to increase your pleasure of ownership then go right ahead. I love to see the standard 'as they left the showroom' cars - it is a tribute to those who enjoy originality, but I also enjoy seeing how people have improved their cars. Chances are, if you use the car regularly, you'll want to improve its capability and safety. If you enjoy going to shows and rallies at weekends and have a second more modern car, you'll probably enjoy keeping your car original.
It is sensible to let the DVLA know what changes have been made to the car (engine numbers and size, brake upgrades etc.) as todays insurnace quotes are linked to the DVLA database and anomalies between what's in the car and what's on the V5 will show up quite quickly. In the worst case scenario, not telling the DVLA and/or your insurers that you have put a bigger engine in the car can invalidate your insurancein the event of a claim. However, classic status in the eyes of the DVLA, is simply an age issue not directly related to what you have done to the car.
To modify

the Duke of Wellington's famous quote '(publish) modernise and be damned' or as I like to think - 'opinions are like a%^e h(*^es - everyone's got one!'
