My thing is to make thm a blm takes retconning for those of you who don't read comics retconning is where you go back in the lore and you change the story so it fits a most recent plot. THM have an astral guild in uldah, the average person doesn't know this. To make them a whm is easy taking into account the astral guild. To make a conjurer a black mage lore wise is easy because they specialize in elements.