I do it all the time. I like to crochet mittens top down because it's easier and faster than knitting. But I don't like the crochet rib cuffs or the FP,BP thing. So I pick up stitches and do my cuffs in a knitting rib. They're a hybrid I call them. Experiment. The worst that could happen is you'll have to frog and use the yarn for something else.