I don't see why you couldn't, but I don't know why you want to. Using the power of shadow can conceal you in the night, conceal certain actions/emotions (good for a job interview if you're nervous), but it also generates a "spookie" feeling because it is the darker side of fire.
Shadows are soul less, but believed to be bound to the soul that it belongs to (native american). Stepping on someone's shadow used to be seen as a sign of disrespect and if a witch stepped on someone's shadow, they didn't need a personal belonging to place a strong spell on them (italian). I remember that I used to be careful not to step on people's shadows when I was a child because I thought I may hurt them. =)
Shadows have a long line of spiritual superstition and belief surrounding them.
I don't exactly know much about all the "shadow magick" talk. I think its just another neo pagan thing. And I don't read that stuff on purpose.
The term book of "shadows" was never even gardners. It was a guy named mir that published an ancient sanskript text that explained ways of divination including divination by observing the shadow of an individual. And he called it "the book of shadows". It was published around the same time as gardners grimoire and its said that garnier adopted the catchy name. I personally think the name is catchy too, so I use it. But shadows were not a huge part of magick, only an aspect of nature that represent darkness in light.