Folks can make all the declarations that want about what they are and who they are when it comes to "race". But they are deluded if they think how they identify themselves resonates in society-at-large if the way the look doesn't coincide with the physical appearances that are associated with Europeans, Asians, and Negroids.
What you think you are is voided by how an unsophisticated world sees you. A person may consider themselves black but if they have fair skin blue eyes and straight hair, they will spend a lifetime, trying to convince people that they are black no matter what persona they adopt. If you have brown skin with frizzy hair and a flat nose, nobody but a blind person is going to perceive you as white just because you say are white by virtue of having one black parent and one white one, and you have chosen to be white. If you have yellow skin and slanted eyes and straight black hair, you cannot declare yourself to be black because you dig Rap music and like collard greens
It doesn't matter what you say you are. People will decide for themselves what you are to them and their eyes will be the final judge, not the superficial affectations of people trying to transcend "reality".