METHUEN, Mass. — For three months, three women from the Merrimack Valley and New Hampshire have been working to train wild mustangs given to them as a part of a nationwide program. The women, all experienced horse trainers, were given 100 days, beginning in April, to train their horses for the Extreme Mustang Makeover, a competition in which mustangs are judged in several categories, including facing several predetermined obstacles. This year, the competition comes to Massachusetts for the first time, as 33 trainers from across the Northeast will gather Friday and Saturday at the Topsfield Fairgrounds.