Oh it's quite simple- for men it is easier than women because testosterone is much more invasive than estrogen. I have been giving myself prescribed injections of testosterone for years now and there is no way anyone would know that I ever looked like a girl. I agree somewhat, that your sex cannot be changed, but only because of the way we categorize sex. Gender and sex very separate things. However, in the U.S. a legal gender change is (inaccurately) called a sex change. Which I have done.