First and foremost, please note this warning from the manual:
Fitting of other purpose or different sized blades will void the warranty.
Needless to say, you are doing this at your own risk.
With the above out of the way, I have run all the tests that I needed: the blade is fixed and has no play (which suggests that the harbour nut is fully threaded as suggested by jdv). The saw has no riving knife so that is not an issue. It does have an anti-kickback mechanism which is a mechanical lock on the plate-rail connection so it still works.
From my tests, the kerf that the new blade leaves behind is 1.7mm along the whole cut (checked with a caliper). The harbour seems perfectly locked in place, there is no vibration and the cuts are straight and square. I must say it seems a weird limitation but I guess it is just that they did QA with a limited set of blades and they don't want to take responsibility over use outwith range.
I have been using the saw with the thinner blade for a while now and it performs beautifully, leaving straight clean cuts every time.