Iris are pretty much bulletproof when it comes to transplanting however the fall is the best time to transplant them to have a decent chance at a nice bloom next year. If the foliage is not cut back significantly at the time of transplanting they will tip out of the ground. Make sure you inspect the rhizome for damage from iris borers. It will look like someone had punched holes in the bottom of the iris. These should not be planted in the new bed but can be planted elsewhere. Many will still sprout new plants that can be harvested the next fall but you don't want to intentionally introduce the borer into the new bed.