Hi Emanuel!
I think it depends on the tire. Some are made specifically for the front or rear wheel.
The sizing is another thing.
My People S 2008 uses 100/80 as front tire and 110/70 for the rear. Both are 16". These are the sizes that stock tires had and now I ride on a different set from different manufacturers but I went for the same size. Probably you can fit a little bit different sizing, but then it's not known for sure if it will fit the bike well.
By the way, you don't have to have a matching pair of tires. I have different tire for the front and different for the rear and it works perfectly.