Movestate controlling unit AI

Use Attack Move. Hold Position causes units to only activate unit AI with Attack Move.

I think technically you're asking for unit AI to flee defenses. Skirm would try to make the units go into range, but if they already outrange the deferences then they will shoot at them without taking damage (except for edge cases like Ronin vs. Stardust, but Ronin already has unit AI vs Stardust to help it keep just outside range).

There is currently no support for swapping in different lists of units with variable settings, but it doesn't sound impossible to add. Adding some state toggles that refine AI behaviour sounds reasonable now that they can be hidden from the default UI. I'd expect some people would use them for Initial States rather than ever toggle them ingame.

I've come around to thinking that the only thing worse than a state toggle is a state toggle with more than two options. At least two options can be thought of as "do this or not", while three requires an explanation of each. It's also more annoying to hit a key or a button twice to get to the state you want. Add more toggles rather than an additional state for the movestate.

Roam is removed by default and the state is simply called Hold Position. It can be enabled or disabled. It is the three-state movestate underneath. The same happened for hold fire.

Yes. Then hide it on the UI.

Then players can configure units with it via Unit Behaviour, or unhide it.

Then add a custom state system which players can use to set aggregate states for their units, with a scalable number of toggles. This configurable aggregate state would be purely luaUI-side, in effect the simple boolean states would become an interface between luarules and luaUI.