Oh, I almost added some comments on Steam last night. Since you're here I'll go ahead.
If the goal was to get them underground, but you didn't want to make (wild, vanilla AI-style ) anthill citadel spam possible, you could start with a unique irreplaceable queen (empress?) commander who has a makecolony command for an Argarthan colonyterr so she can found one new proper underground colony before settling down to just be a housequeen - or even just given her and her alone the citadel-founding ritual so the spread is limited to how far she go. If you didn't want an irreplaceable empress, you could also add a promotion ritual with nomonmasteryreq restrictions so she can only be replaced, never duplicated...
(It also occurs to me that them not starting underground will make them more resilient - if pale ones accidentally flood their tunnels, they can keep playing... but ants wouldn't have that luxury...)
Actually, you can't mod the starting positions at all and the startplane command doesn't work. The next update will add that in when they fix startplane mod command, but no idea when that will happen. The mod would actually work better if the ants were underground.
With that said, there is the princess who can makecolony randomly. I thought of giving it to the queen herself, but a queen would already have a colony and a princess would be a new colony. I tried it and its pretty random, happened twice but then never again so I'm not sure if something happened and it broke or what. I assume it still works. I have no idea how to mod the makecolony command to only work in one place, but I'm actually ok with it as it is since princesses "retire" after making one colony. And do want stuff happening on the surface too. Also. Funny enough, anthills outside of the starting one produce ants
The AI also doesn't actually tunnel (even with the command they won't use it), so the whole theme of the mod that relies on being underground is a bit messed up sadly until the startplane command works
When the AI DOES go underground, it functions as it should. But they won't tunnel on their own (they do dig once underground though).
As for wild surface issues. Well until they start in Argatha, that is actually a problem sadly.
I do like the idea of a single queen with only a princess being able to take her position though, I'll keep that in mind for the update following them starting in argatha. If that even ever becomes a thing.