*ahem* for those not in the know, Hayate Yagami is the only one left in her biological family. She's technically an orphan in the Nanoha franchise, but I made up parents for her for the sake of the story (as well as a fake background story).
About Kariya and Byakuya switching places, Zouken can't do that. He believes that Byakuya's line is devoid of Circuits, so he has to trick someone else into getting the Grail for him....
...namely Makihisa Tohno from the Tsukihime franchise.
Besides, a different change involves who summons Caster, namely Ciel (around the time after she survives Roa leaving her body). No, wrong Caster in this war, it's not Bluebeard.