I'm not sure where to mod in rain that makes you sleepy, since I don't know where the entries are that makes for evil mists and evil rain, but if that were (or is) player accessable, then it would be easy enough to just copy and change the name, syndrome and biome tags.
I like the idea of Angels instead of Demons in the underworld of Good aligned regions, with not much other than a name and description change.
I lke the idea that dwarves would (should?) need an attribute (like laziness or helpfulness) that reflects their own personal good/evil alignmenet to be attacked by surface good critters, so that Beings of Good would attack anyone who doesn't meet their personal requirements for Goodness. Consider, if you will, if You Personally were to meet an Avatar of Good (even a minor one)... would you not fear that perhaps it would smite you for your own petty (or not so petty) evils? Why should dwarves fair differently? And for those who perhaps think that additional Fun stuff should be limited in Good aligned areas, maybe put in the init files a way of controling that.. I'd put it in the same place as disabling weather, tempurature, moods and such. Maybe say something like "Dwarves Judged on Alignment - YES/NO"...
Or perhaps coming into contact with such a Being might (over time) change such things as helpfulness and courage, though that might be a harder thing to code. (Being a modder, not a programer, I don't actually know.)
Ok, this has sparked some thought in me... I will consider it in more detail so that I can maybe add something that doesn't sound so disjointed.
The moving plant things is easy-ish, though.. simply create some animals, mod to have specific plant tissues instead of meat tissues, and (if you like) set their movements to something incredibly slow. (Check out bronze colossus and wagons to see how they work, if you need some hints.) You can make them highly agressive without making them savage. ... or quick, for that matter. I have several, the vermin of which drop plant seeds instead of small remains, and the larger of which drops logs. I like to use the related tiles from the plants on which they're based to give the appearance of slow moving plants. I especially like making them bleed booze. I would like to make them change any blank soil they walk over to having grasses of that type, but I suspect that requires hard code changes. Putting in the grazing tag with a negative number fails... I now assume that that number reflects how many time units pass before a creature eats (which explains why bigger creatures have smaller numbers). Pah. If someone else figures this out, let me know, k?