All these things need not to be coded. If a ruler/realm behaves in a particularly bad way, it will have some consequences. And if it has none, then he played it right.
particularly bad was is, for instance, when alliances A and be fight, alliance A suffers series of losses, than some realm that are part of it quickly change side, and we have gang-bang war.
would such ruler suffer consequences? no, he would likely enjoy additional benefits. consequences too often fall on those who behave excellently. i saw more than one realm which ultimately disappeared because their rulers did not accept awkward diplomatic changes which were not justified by anything but mere desire to save the throne.
in that respect, i believe that current game mechanics to some extent encourages
too flexible pragmatism. medieval history does not actually remembers too much of those who survived ,after they are defeated, because they are pragmatical.
if harakiri is not expected from european rulers, they were at least expected to die in battle, or go to exile to the end of their life after they are defeated, not to quickly change diplomatic stance and stay on throne.
