If the sapwood is still good, give it a go. If not, take it down to a clean heartwood ring, do your best to chase a ring, which sometime seems impossible with yew, but some violations won't hurt. If you aren't going for a really long draw with a short bow, you don't absolutely need to back, other than piece of mind, but if you are concerned, rawhide back it, or whatever backing you like, raw hide backing is just quick and easy.
Eric