Well you could, When cave-adaption hits 0 BAM stone. Altho does non controlled creatures suffer Cave Adaption?
I'm speaking for Balrogs of course, altho. Would a demon turn to stone? Might work for trolls if you make them a underground civ or wandering critter
But underground critters have a tendancy to try and leave through the surface...
I don't think Balrogs turn to stone in the sun at all; they're quite too powerful for that.
Also, does cave adaptation ever go down? Besides that, there's the issue that all these creatures will be born/spawned with a cave adaptation value of zero, which would ruin them all. Trolls would show up at your doorstep turned to stone, etc.
It just wouldn't work.
Also, I'm currently working on a Sindarin language file BTW.
If you use the REQUIRED tag (which is the only way I've actually seen COUNTER_TRIGGERs used) and a syndrome that activates at 0 and has no maximum value, the Cave Adaptation syndrome will be active whenever the creature is actually in the cave, regardless of its value, and shut off the moment they go outside. So what you could do is make the creature non-viable by default, and then give them an additional cave adaptation-linked syndrome that makes them able to survive.
Like (for instance) you could make the default creature a statue with no brain, then give them a cave-adaptation syndrome that turns them into a viable form whenever they're in caves. Leave the cave, and they'll revert to stone and die. As long as they spawn in a cave, they should be fine until they go outside. (They'll need a few frames to apply the syndrome in the first place, but I'm pretty sure brainlessness doesn't kill instantly, it just suffocates the creature.) Alternatively, if the 'X has transformed into an Orc' messages are a bother, you could make them aquatic and immobile on land and make the underground give them NOBREATHE. Or just make them without lungs.
None of this will be affected by day/night cycles though...unless...really weird idea but...if you use the monthly COUNTER_TRIGGER as a time-setter and make the syndrome go on and off each day... (set to Adventure Mode time, since days are pretty much immaterial in Fortress). They won't be smart about it though, and that means you can kill an entire Orcish bandit group just by walking into their camp during the day
I guess they should just be underground and forget the whole day-night thing.
And yes, non-controlled creatures do have Cave Adaptation, even in Adventure Mode. I've tested it. They also seem to spawn with a random value of cave adaptation when you find them in Adventure Mode, although that would be immaterial with this method.