Very interesting effect.
This is one of the images that I'm trying to change to gold.
Also, I need to turn it to" copper color" like it was a electronic circuit, but for me it's getting very difficult to create a realistic and shiny effect with my basic knowledge. That's also my reason for asking for a plugin.
I tryed to use the plugin you suggestd with this same image, but I don't get the "gold" you achieved. I believe if I turn this image to gray like your trophy, maybe I will see the effect, right? I tried with other gray images I have and it was fine. I see I can use it for another project I have.
I'm still looking for a more realistic and shiny gold effect for the image I uploaded here.