"If you were designated male at birth, you must register for the Selective Service if you are between the ages of 18 and 26, even if you have had sexual reassignment surgery. You may register online at
http://www.sss.gov/default.htm or you may complete and mail a "mail-back" registration form available at any post office. In the unlikely event that the draft is resumed and you receive an order to report for examination or induction, you may file a claim for exemption from service.
While you do not need to notify the Selective Service of a change in gender, you are obligated to inform them of a change in name. To notify the Selective Service of your name change you must fill out Form SSS 2 (technically a change of address form), available at your local post office. You must attach a certified copy of the court order changing your name."
This is the passage listed under MTFs and Selective Service in the name/gender change packet I got from my lawyer last week. Hope it helps.