And I think you're trying to explain the clause in a way that simply supports your side of the discussion. You seem to be assuming that a service agent only undertakes a single function 'servicing' but that is just not true, they also undertake installations. That aside, the important word in that clause is 'Modifications'
The item in question will come with moulded plug top, by cutting off said plug you are thereby making modifications to said item. If the person doing the modifying is not trained/approved by Miele then you have just killed your warranty.
Now this bit might strike you as strange, but I would really love for you to be right and for me to be wrong. Miele might be an exception, as they pride themselves on service, and if your going to be paying the sort of cash they ask for their white goods then I should blinking well think so too.
However, I consider insurance legalized theft, and warranties are simply another form of insurance. I just know from previous insurance claim dealings that I have had in the past, that these 'slipperier than an eel coated in fairy liquid' persons with disputed lineage, will screw you at every single chance they get, and if they can twist what is written to work in their favour then they will.
So in summing up, I understand what you are saying and to all intents and purposes I agree, I just think that the world we presently live in means companies, and the bean counters that now run them, will always carp on the little guy from a great height if given half the chance.
And with that waffle over, I'm off down the pub.
Cheers