Yes sex changes should be legally recognized if a person has gone through the extreme amount of effort it takes to fully receive a sex change. It is there right to be who they want and they should be recognized as such in all legal standings. It would be discrimination if otherwise.
Gender and sex changes should be legally recognized. Just as people are born with specific sexuality, whether it's gay, straight, bisexual, queer, etc., people are born identifying with a gender. Transgendered people are often very intuitive; they know that they are in the wrong body. Allowing people to be recognized as the gender they should have been born into is ethical and humane. Many transgender youth go through a tremendous amount of anxiety and personal tribulation; we owe it to individuals to legally recognize their true beings.
Sex changes change appearance. They do not change your internal reproductive organs. A man gettng a sex change will not be able to give birth. That being said, sex changes are only for appearence and should not be recognized by the law, just as tattoos aren't. There is no difference.