Should the Congress and the President reinstate a draft, a classification program would begin. Registrants would be examined to determine suitability for military service, and they would also have ample time to claim exemptions, deferments, or postponements.
To be inducted, men would have to meet the physical, mental, and administrative standards established by the military services. Local Boards would meet in every American community to determine exemptions and deferments for clergymen, ministerial students, and men who file claims for reclassification as conscientious objectors.
Are disabled men, or men with medical conditions, required to register with Selective Service?. The only process now in effect is that men between the ages of 18 and 26 register with Selective Service and keep their registration record current during that period. Neither the Military Selective Service Act nor the Presidential proclamation provide an exemption from registration because of a man's mental or physical condition unless Selective Service is provided with documented evidence that the man is hospitalized or institutionalized; or home-bound and unable to function outside the home, with or without physical assistance; or is in such a physical or mental condition that he would not comprehend the nature of his registration with the Selective Service System. A determination is then made by Selective Service as to whether or not the man qualifies for exemption from registration.
http://www.sss.gov/qa.htm#questaaI also found this rather peculiar rule. Does this mean that a transgender woman gets drafted as a male if no exemption is claimed?:
How does the Military Selective Service Act apply to individuals who have had a sex change? Individuals who are born female and have a sex change are not required to register. U.S. citizens or immigrants who are born male and have a sex change are still required to register. In the event of a resumption of the draft, males who have had a sex change can file a claim for an exemption from military service if they receive an order to report for examination or induction.