Recently, I found a reference online to a New England Journal of Medicine article dating back to 2004 which dealt with genital reassignment surgeries performed on patients suffering from Cloacal exstrophy which is a severe birth defect that occurs in approximately 1 in 400,000 live births. One of the most pronounced characteristics is severe phallic inadequacy, or the complete absence of a penis in genetic males. Historically, doctors have treated cloacal exstrophy by surgically altering, or "reassigning" these babies as female.
John Gearhart, M.D., director of pediatric urology at Johns Hopkins Children's Center and an expert on exstrophy complexes, and colleagues challenged this standard treatment by studying 16 genetic males from 5 to 16 years of age, 14 of whom underwent surgical conversion to female sex. They found that more than half of them identified themselves as male; six individuals were so unhappy with their female sex of rearing as to pursue gender reassignment back to male. All 16 had interests and attitudes that were considered typical of males.
This leads to once again to fortify the idea that gender identity is primarily rooted in the brain and that performing genital reassignment on non dysphoric individuals will not change their internal sense of who they are.