grand alliance armies and allies

[Evangelist of Cinders]

So, I have a re imagined hyshian bretonnians I'm working on for a local campaign.  I as a result need to make it a Order army using the generic abilities. I really wanted to do some crazy conversions (sadly can't use any of the new cities of sigmar battalions even as allies)   and was looking through the rules and in the basic rules it says allies can be from a different grand alliance and my conversion loving mind went wild. I don't have most recent generals handbook but couldn't find a rules for a pitched battle profile for a just order army and am wondering could I take say a Chaos unit as an ally? I'd love to make crystaline creatures represented by Chaos spawns, or even build the PReyton i've had gathering dust since the world-that-was.

[RedMax]

I suppose you are looking for mercenary options.

All that is in GHB2019. I don't have it with me but this is what I'm remembering about it.

Like Allie but could be across different GA. Anyway, this is really specific set of warscroll only that could be used as mercenaries when allies could be any warscroll but from a precise (allied listed) faction.

as example, any army ay take a necromancer and some skeleton as mercenary. Mercenary count into allied points, prevent you to get 1st round command point but give you a special ability for mercenary "battalion".

[EMMachine]

The corerules allow allies from a different allegiance. And the grand Alliance has no restrictions for allies like more specific allegiances have. But it's more likely a narrative thing