You CAN powder coat over chrome wheels, but I wouldn't recommend it. Depending on the quality of the chrome finish the baking process of powder coating can cause damage and/or weaken the chrome, making the overall finish less durable. Picture a powder coated finish now applied over chrome that may eventually start to corrode, pit, and peel, thus taking the powder coat with it. Make sense?
If you don't like the chrome rims I would highly suggest going to a different rim all together, I wouldn't waste money changing the color of a chrome rim, whether powder coating or painting, the end result just won't be durable and won't last. Then you'll be left with rims that aren't even worth trying to sell.