Snow tires on the same rims?

I have a '14 Ford Focus riding currently on the factory wheels and rims size 215/55/R16. Can I use snow on those rims?

Sure you can. There are a few in your needed size of 215/55/R16 which are very good quality. They will all fit your factory rims perfectly.

You could but you'll pay to have them changed over twice a year. Much simpler to have a second set of steel rims with your snow tyres. Keep them in the garage.

Yes it is possible but you could go to an auto salvage yard and buy used wheels for $15-$20 a piece to mount your snow tires on. That would make the annual change over easier.

If you want snow tires you will pay $80 x 2 =160 per year to take them off, you really can't drive snow tires in the summer. Maybe look at some all season Cooper or Mastercraft tires.
Or go to tirerack and buy snow tires and steel rims. They are already mounted and balanced.
Get the equivalent 15" size tires, they will be cost less and thinner so will work better in the snow.
Tire rack can tell you what size to get.

Umm, of course. Any tire of the correct size will easily fit on those wheels. The wheel does not care what the tire is.