I have double pierced ears and very short hair, so my earrings have always been a target for my parrots. I'm still working with my senegal about it, but when I still had my sun conure, she had gotten pretty good about leaving them alone. The only thing I ever did with her was, when she went after them, I would turn my head (to move the ear and earring away from her) and say "no earrings". She liked to pick around at my ears, so she *most of the time* left the earrings alone probably because picking at an earring meant the whole ear got taken away. ^_^
I can imagine that birds could do a number pulling out a piercing, though neither of mine ever has, but one thing you want to keep in mind is *infection*. Even though she was usually good, my sun picked at one or both earrings (close to the ear studs) at least once a day, and the pierced holes in my ear frequently would get infected from it. So my first advice for someone whose parrots do pick at their earrings would be to make sure to take some extra time with rubbing alcohol to clean both ear and earring well at the end of the day and/or play session. (It's also worth noting that I got fewer infections when I wore small hoops, where her beak wasn't in direct contact with the pierced hole when she picked.)
-- Morgi and Bijou, good bird
