You can, but it’s not necessary. The brine may become clumpy and won't add as much to the flavor and texture of the cheese. If you want to use a brine, a better habit is to thaw the cheese and place it in a brine of salt and water as soon as it is thawed. This will help restore the salty flavor and delicious texture of the mozzarella that is often lost when it is frozen and thawed.