Yes, there is such a law. A eunuch, either deliberate or accidental, may not convert to Judaism.
And it could apply either way, depending on definition.
If an M-to-F transsexual is a woman, then the law about a man not being able to convert isn't relevant, because she's a woman. But if you go by chromosomal sex, then only a pre-operative transsexual can convert.
Similarly, if a F-to-M transsexual is counted as a man, as he is, then he would count as a man who was born castrated. And that's a separate category in Jewish law than a man who has become castrated; I don't think there is a prohibition against the conversion of a man who was born castrated.
I would make the further argument that the existence of a category of men who are born without testicles could be noted as an acceptance of the existence of men who are born without male sexual characteristics, and therefore an acknowledgement of F-to-M people. Further, there is the category of tumtum, who are people born with ambiguous or indeterminate gender.
no subject
And it could apply either way, depending on definition.
If an M-to-F transsexual is a woman, then the law about a man not being able to convert isn't relevant, because she's a woman. But if you go by chromosomal sex, then only a pre-operative transsexual can convert.
Similarly, if a F-to-M transsexual is counted as a man, as he is, then he would count as a man who was born castrated. And that's a separate category in Jewish law than a man who has become castrated; I don't think there is a prohibition against the conversion of a man who was born castrated.
I would make the further argument that the existence of a category of men who are born without testicles could be noted as an acceptance of the existence of men who are born without male sexual characteristics, and therefore an acknowledgement of F-to-M people. Further, there is the category of tumtum, who are people born with ambiguous or indeterminate gender.