I've done a couple, but nothing that I was concerned about messing up on. Certainly not an expensive custom barrel though, like a Shilen. the few I have done came out looking good, but they required touch up over the years to keep them looking good due to chips, scratches and what not. Any more though, cosmetics don't fit into my list of things to maintain on most of my rifles, wood stocks are the exception. I focus my attention on keeping them functionally well maintained.
As for handgun, I do like to keep them looking nice. And it's a constant task, as I use my handguns a lot, and also carry them often, so they do get scratched and dinged up.
What's wrong with it? just don't like the color or trying to match it up cosmetically or something?
If it were me, I would probably take it to a good smith and have them do it, other wise you could end up having to have it completely stripped by a professional, and then added costs as a result.
But to each his own.
GS