Whatever you do the the brass, or copper, mods, other than coating them, they will patina, a nice word for tarnish which is a nonscientific word for oxidize.
The stainless steel also oxidizes but it produces an oxide of chromium that is clear and protective.
For the mods you already have you can let the brass just patina or Google brass patina and do it quickly.
Stainless has a few choices. You can flame it, which will turn it shades of gold, blue, purple, etc., depending of what temperature you get it up to. Do NOT do this to any part that has a plastic piece you can not get out cause the temperature you need is far above the melting point for the plastic.
You can take sandpaper and turn it into brushed stainless. I have used grits from 80 to 400 to get different finishes.
Take it to someplace that will blast it.
Google is your friend with making metal look different. There are a lot of craft people who do strange things.