I can't speak for ticket rules, but the Shareholders discount goes on a similar way to an MCO, hence it DOES NOT change the fare rules at all (as it says in the shareholders T&Cs) and given that a T-class of any flavour is upgradeable, so a T-class with a S.D. is too, except for the fact that the same Shareholders T&Cs ban it, in direct contradiction to the previous entry...