it's probably a sin to have a sex change since god made you exactly how he wanted you or something, but according to faith, as long as someone looks lke they are part of a normal heterosexual relationship, her sensibilities aren't offended and it's thus not a sin. but, being that faith is not the person who defines sin (despite her behavior if not claims to the contrary), i'd have to say it's more of a software problem. though clearly, if the act of anal sex is the problem, then it is a hardware problem. specifically, it appears that the problem is the lack of a vagina that must be tamed.
of course, certain people have also stated concerns related to the ability or inability to have children. people who have had sex changes cannot have children.
i'd have to say. since god made a specific command for the jews to number as the stars, it might be a sin for a jew to have a sex change. but it would probably not be a sin for a jew (who is not a priest) to be gay as long as he or she also has children. however, god has made no such numbering command to the gentiles.
but there is still the whole body is a temple thing. but then also all plastic surgery wold have to be a sin. also, piercings, tattoos, hair dye, perms, makeup, and so forth.
but that is just my opinion based on literal understanding.