According to the punahou yearbook his name on his graduating photo was Barack Obama. I don’t think he used Soetoro in high school. I think he was called Barry at Oxy but still with the last name of Obama. It was very cool for blacks to have African names. He was really trying to be black by that point.
But there is a likelihood he used his Barry Soetoro passport from Indonesia at age 18 when he visited “Pokkistan”.