Our Blue and Gold x Red Fronted was as wild as they get when we got her. Every time you walked in the room she'd fly around screaming. Then we got her wings done and started gently working with her and building trust. She will still nail everyone in the house but me, but when she bites, it's not quite as hard (more of a pinch).
I found the key was to teach her what 'NO' meant. If she charges me to nip, I firm no and I snap my fingers at her and she'll go back into chill mode. It's all about patients with Macaws. When you say a word, make sure it always has the same outcome. Once they learn that word has a meaning and they disobey it, they'll learn not to take the action that results in the outcome.
For instance, you say 'NO', he bites anyway, walk out of the room and ignore him for an hour. Before I started working with her, she'd split two of my nails in half and her biting hard enough to cause bleeding was an everyday occurrence. She hasn't bit me at all in months and if she nips someone else in the house, it's usually from playing too rough.