Look, it's simple, you reverse the plating process simply by reversing the terminals on the plating tank, so it takes the current plating off. It needs to be done firstly for the chrome, then the nickel. You are left with clean brass. It is a benign process. Then the nickel is applied to the stripped brass, and it depends on brighteners being put into the nickel that decide if the end chrome is satin or bright/ shiny. If the plating company don't understand this they are specialists in something else, not the plating you need.
It is possible to by your own chrome plating and nickel plating stripping kit, and it is possible to buy your own nickel plating kits. It is not possible to buy a proper chrome plating kit, but you can buy cadmium plating kits that do a similar thing if not to the original colour.
Steve