[llamabeast]

A War Altar would be much better done as a unique summon. There is no problem with making new unique units.

The idea of making a unit which changes on being prophetised is quite cool though. I think the best thing to do would be to create a new unit for Abysia, exactly the same as the Abyssian Warlord, but obviously without the special propheting thing. Then Abysia would be left essentially unaffected (apart from losing one little cosmetic feature), while you would get to do the cool thing with the Prophet of Sigmar.

I personally am very keen on having all mod nations be compatible with all vanilla nations (ideally even those in other ages). I think both me and Sombre like mixing the Warhammer nations with the vanilla nations.