Posted: 10/10/2014 at 19:02
Hi Peter, yes you can and many if not most commercially grown grapevines are grafted. Bud grafting is often used and there's some helpful photo's of that on this site:
Google "how to graft grape vines" for a huge amount of information and some videos showing the process. Late Summer would be the best time and, above all, avoid cutting into vines in early Spring before the leaves appear as they will bleed profusely which can lead to their death.