Is is possible (and necessary) to anneal nickel plated cases? If so, how?

It depends on how many times you have reloaded then or are the neck cracking. If not there is no reason to anneal then. If you do than get a pan and fill it with water half way up the case and take a torch and heat the necks until they are dark red and then tip them over in the water that way you anneal the part of the case that needs it and not the whole case, because if you do the same to the bottom of the case you will start blowing primers. Good Luck

It IS possible to anneal. ALL brass requires annealing to maintain it's elasticity and insure top performance of a load. Heating any brass to "red" insures you will overheat it and probably ruin it.

It is not recommended to anneal plated brass but it can be done. The plating at the neck, and further down, will burn and give off a noxious smell. It will also look awful. It will also be more difficult to distinguish the right color and amount of heat to apply. You can alleviate that by turning the plate off the neck portion, but the plating will still burn into the shoulder/body area. It is annealed, with or without plating, just as any unplated brass.