Hey,
Me and my friends faction changed a week or 2 ago and today we found a small exploit that can help with the 100mount achievement.
we went from ally to horde and he had bought Reins of the Wooly Mammoth - Item - World of Warcraft from the vendor, he went to the same vendor while horde and he could learn the horde version and the ally version doesnt get changed into horde.
so 1 extra mount.. we checked with other mammoth mounts but they all get changed into the other version on faction change
alliance one is blue and horde mount is red :>