I know what they're call, as well as the long nose developing as the fish gets larger, more less noticable when the fish is small. Most place leave off the part. about the long nose, and just sell it as a Black Tang, as it would be a turn off if people saw what the adult looked like.
The ones growth in the home aquarium are just as ugly as the larger ones taken from the ocean. Growing one in the home aquarium doesn't make it better looking than getting a large one from the ocean, stress or not. Also if you feed the fish correctly, it will get large. So you can't stop it from changing over into the adult colors, though some Juv fish never fully change into the adults colors, the Imperorer Angel is a good example, as the Juv raised to adults are usually never as colorful as the adults taken directly for the sea.
The stress issue in time wouldn't be a factor, unless you plan on putting a large one in a small tank. If you go to places than have show tanks, like hotels or resturants, or find someone with a large tank, you'll see that the fish isn't stressed out and still looks ugly.