I've definitely seen chrome plated coins. I probably even have a couple somewhere. I'll keep an eye open for them. No legal issues that I know of, as long as it's not done for fraudulent purposes.
Terrible to do to a trade dollar, but the most inexcusable polished coin I ever saw was at the Metropolitan Museum in NYC. It was many years ago - I forget if it was a pine tree, oak tree or willow tree schillings - but it was in with some colonial New England silver. It looked like every time they polished the hollow ware, they polished the coin, too.
