Freezing string cheese is not recommended because it can change the texture of it and make it less stringy and easy to peel.
But you can freeze string cheese if you want to though as it will extend it's shelf life in the freezer.
Although if you do freeze string cheese and then thaw it and then refreeze it then the texture and taste will be changed so it may not be as good tasting as it would be before.
Usually refrigerating the string cheese is enough and then eat the string cheese before it's use by date or before it goes bad.
So yes you can freeze string cheese but for best tasting results it's not recommended.