Yes, you can shred raw potatoes for a hashbrown casserole recipe. I would recommend shredding them onto a cheesecloth or paper towel to remove some of the moisture as you go. Mix them with the other ingredients quickly, so they don’t turn brown on you.   Blanch homemade potato shreds when you plan to make ahead and freeze a hashbrown casserole recipe (uncooked). Blanch potato shreds in salted, boiling water for one minute, hit the ice bath, and drain well.