[Foodstamp]

There is no command for it. Thilock is suggesting that you choose the nation number for Ermor to mod. Then you modify the spawned creatures using #selectmonster for all the creatures autospawned and modifying them.

Alternately, you could modify a spell that autospawns units like Carrion Woods, Haunted Forest, or the one that spawns vine men in your dominion. You could modify the units spawned by the spells just like you would for Ermor, then change the spells casting level to 0, modify the name and the description of the spell, then you would get the desired effect, although not as elegantly as the way Ermor and R'lyeh's effect work.

Finally, you could just create Immobile "gate" units that #domspawn in the provinces they are summoned too.

So there are several ways to do what you want to do. Goodluck.