If you want to use the Plum Brown, set your wifes oven to 260-300 degrees F and let it warm up.
Put your frizzen on a cookie sheet and place it in the oven for 10-20 minutes. Take it out of the oven, rapidly go outside and apply the solution. Zap! It's brown.
300 degrees will not effect the hardness in a way that would hurt the function of the frizzen.
If the frizzen was not heat treated properly by the maker, and is too hard, 300 degrees F will toughen or temper it and help prevent cracks at the screw hole and at the base where the vertical leg meets the pan cover portion. Repeated heating to the 300 degrees F temperature will have no effect on it.
Don't heat it with a torch because you have little or no control of how hot it really is getting and you may heat it up into the 400+ degree F temperature range where it will start to effect the functional hardness of the steel.