Short answer: a clone counts as a younger sibling of the genetic donor.
Longer answer: Generally a clone (commonly called a true-child) in most cases is treated like a younger sibling for the purposes of inheritance. Free clones, like Seldarian, are those independent to develop their own personalities. In one case in GT: Nobles, it is mentioned that a title in the Solomani Rim is preferentially passed to clones over naturally conceived children.
As for the biotech end of it, I would suppose that it would be easy for geneticists at Imperial Tech Levels to take a donor's genetic material and replace one sex determination chromosome with another, preferably from a related party. It also sounds like the genetic aging items may be fixed as well.