What do you mean? Changing the train consist during the trip? That is exactly what they can do.
Hamburg/Amsterdam on one end, Innsbruck/Wien on the other. Those wagons get shuffled about like a deck of cards en route! So in Amsterdam there is one train with wagons marked Wien and wagons marked Innsbruck. You get in the right numbered wagon, and end up where you want. In the middle of the night, in the middle of nowhere (actually, probably München) they turn two trains into two different trains.
Where I live it's a pretty common feature of train timetables - certain trains will split partway through a journey, and no-one gets off in the process (well, unless part of the train is terminating at the stop)
