It is possible to change many features of your body dramatically. Plastic surgery can re-shape your face, give you bits and take away others. There are a few post-op transexuals who look absolutely amazing, but the hard limit is the skeleton which decides our basic proportions and can't be adjusted (though chins can be rounded off and ribs can be removed). Going from female to male is even more difficult as there aren't many ways to make new bits and build up chins and the like.