Wheels for the current Swift Sport also smaller than 17″ possible?

Can someone tell me without having to run to the dealer first, whether you can drive on the current Suzuki Swift Sport rims smaller (the original) 17″ without registration? If it goes without TÜV entry. My wife gets yours in a few weeks and for the winter I would favor 16″ rims. And if I am just asking, there are also 16″ steel rims for the Swift Sport? Nice greeting Clive