Shaving the coat, unless you completely shave to the skin (which I would DEFINITELY NOT recommend EVER), is not going to reduce shedding. Shaving does not actually get rid of any hair that is going to be shed by the dog, it just shortens the hair. They still have the same amount of hair to shed-- the hairs are just going to be shorter (and sharper since cutting makes a sharp end to the hairs.)
If you want to reduce the shedding you can try a shedding blade or Furminator, or go to a groomer who does the Furminator treatment. I do that with Bianca to cut down on the shedding in the summer and it helps a lot.
Shaving a long coat won't make them look like a regular/stock coat German Shepherd because most of the color is at the tips of the fur, plus shaving exposes the wooly undercoat. So shaving will make the dog's fur color look diluted or lightened and their fur will look wooly or fuzzy.
Shaving a double-coated breed can actually make them heat intolerant as the double coat protects them from the heat and sun. There is also a risk of sun damage to the skin.
Example here is a shaved (stock coat) Shepherd, see how the fur is lighter and the black saddle is gone?
Here is another, you can see the wooly appearance to the coat here:
