No, this is not necessary. Anabolic/androgenic steroids all work primarily by attaching to and activating the same receptor. As such, you do not gain anything by switching to a new compound that works via stimulating the same receptor. If tolerance were induced by one AAS compound, it would be extended to all compounds. The plateau effect that is noticed 6-8 weeks into most cycles is poorly understood, but likely related to the new metabolic limits placed on muscle cells under the influence of a certain AAS dosages, not insensitivity to AAS. Classic downregulation does not occur with these drugs, and even if it did, rotating steroids would not prevent it.