[Burnsaber]

For MA Alchera, I'm thinking about having a number of sacred Moko warriors, based on their whakapapa (geneology/ family history) - they'd have different on-bless specials to reflect their whakapapa. I'm also thinking, once I get Taniwha worked out, about having a "Ritual of Rebirth"-like water + divine spell that allows the caster to be reborn as a Taniwha after being killed, as the possibility of becoming a Tanwha after death is a really interesting part of the myth for me.

Llamabeast is right, you really can't do these things as you advertised. But here are some mod haxing ideas.

You can't really mod Twiceborn, but you could make it national for MA Alchera and change it's paths and alter the wight mage unit. This would, however, take away twiceborn from all other nations.

About the Moko warriors, you could mod a different types of blessing spells. Like that Moko Warrior caste A has a corresponding Priest with a modded blessing spell. Since blessing spells don't have any effect once the target is blessed, the Moko Warriors could only take benefit from one of these spells at a time. There isn't any way to make caste A blessing blessing ignore caste B (unless you're willing to give them strange tags, like undead/demon/magic being/amphibian). But you just could make the blessings rebundant gameplay wise. What if the caste B & C blessing spells give something that A has already? Then there really wouldn't be any reason to use cross-caste blessings.

About Taniwha, you could make it like the "Banquet for the Dead" for Ashdod. It would kill the caster and summon a Taniwha (reincarantion of sorts?). If you're intrested, I suggest you PM chrispederson (or was it chrispedersen?) about it, he did some testing with modding the spell effect a while back.