My answer to devastating charge question would be, "When do you resolve the devastating charge?" I've never played with a unit that has the rule so I'm not familiar with it, but I'm guessing in the close combat phase. As the magic phase comes first and the spell grants the unit devastating charge, the unit then has it in the close combat phase and you resolve its rules then. Simple as that, if they have the rule, you use it when you are allowed to. It doesn't matter that they got it after they charged, only that they have the rule. Also, as it is not a remains in play spell, it would be pointless if it didn't work in this manner as the unit would lose the rule prior to the closecombat in the the next turn.
The Transformation of Kadon should definitely work like the Apocalypse transformation spells. Once a model is reduced to 0 wounds in the other form, it reverts back to its wound level it was at prior to transforming and the spell isn't remains in play.
I'd have to say that the intent was not for detachments to get 3 attacks from the Word of Wrath, but it seems they can, assuming Grand Battle Prayers are passed on to detachments like normal Battle Prayers. Technically these aren't Battle Prayers and as the rules state that only Battle Prayers are passed on to detachments, it could be argued that these don't and the detachment only gains +1 attack due to being within 12". There is nothing in the Grand Battle Prayers section that says they are or are not passed on to detachments.