My group recently acquired "First Founding" and my Blood Angel player is *highly* interested in becoming a Tyrannic War Veteran. His IC logic is, as the Blood Angels deployed several companies to assist during the second(?) Tyranid war it would be possible his character learned how to fight the Tyranid sufficently to take up the speciality.
Opinions? While I see the point he's making that we could House-rule this sort of thing, I'm not sure this is a floodgate I want to open.