Ten stakes races will be conducted on the star-studded opening week at Keeneland in Lexington, Ky., with plenty of runners hoping to move on to the Breeders’ Cup. But the most popular Thoroughbred in competition in Lexington this week might be a few miles away at the Kentucky Horse Park as several hundred retired racehorses vie for their own rich prize. Cozmic One, the first foal out of immensely popular Hall of Fame racemare Zenyatta, is one of nearly 500 Thoroughbreds expected to compete at the Retired Racehorse Project’s $100,000 Thoroughbred Makeover and National Symposium, set for Thursday-Sunday.