[Maraxus]

Sadly, the usual "is it possible?"-answer:
No, not possible.

And it also looks to far of from the current game to come in in a later patch ...

Well, maybe the first could get somewhat realised. There are magic sites that give a conjuration etc. Bonus. Maybe in a futur patch this will be doable in a mod and maybe negative numbers could be used to increase the cost and a last maybe, the negatve maximum will increase the cost to infinity, resulting that ritual spells of that type are prohibited in this province.
But right now, this is impossible, too.