While I've never shellacked a cookie, I've been asked many times if it would work. So this is a very interesting topic! I had one lady who kept a couple of my 3D cookies in plastic baggies (the Raggedy Ann and Andy in my clips). When one of her grandkids got hold of them, she damaged Andy. I was asked to repair him as best I could, and it turned out pretty well. (Especially considering the cookie was over two years old at the time!)
P.S. - I LOVE those gorgeous red hearts, Aniko!!!!