stoble, When I had my gunsmith shop, I had several customers bring in nickel plated guns to be restored. When I quoted them a price, they didn't waste as second saying "no" Here's the process: First, if you want the gun to look nice, you would do the whole gun, not just the cylinder. Why? As nickel plating ages, it changes color so a refinished cylinder would not match the frame. Next, the nickel plating must be totally removed before replating. This is not an easy process because you really can't use tools or you will damage the gun. So the first step is to "pickle" the entire gun in an ammonia tank. After an overnight application, some of the plating will peel off but most will not so you have to repeat the process at least 3 times, maybe more. When you finally get all the nickel and copper plating off, it's time to plate the entire gun (one piece at a time) by electroplating with copper. Once the entire gun has been copper plated, finally you can chemically or electroplate all the pieces with nickel. This adds thickness so it always causes problems with fitting parts so you may have to spend a lot of time fitting parts to make the gun work again. I did not have nickel plating equipment in my shop so I had to farm out the work to a specialty shop. Actually, it's much easier and cheaper to nickel plate a blued gun because bluing is very easy to remove .... just a few minutes in an acid bath and you're ready to electroplate with copper.
BTW, nickel plating guns as become a lost art. Very few shops are equipped with the proper equipment so most guns are plated in specialty shops that charge a small fortune.