If you don't want to sand or strip your light oak bookcase you could consider some gel stain. You will have to do some light sanding with this product but it won't take you long! Here's a bit of information regarding gel stain. https://www.diynetwork.com/made-and-remade/make-it/get-to-know-the-magic-of-gel-stain
I used a Rustoleum kit to change a white cabinet and a blonde cabinet to the dark wood grain color and it worked beautifully.