At now, We can only control the NPC spawn by setting spawn weights ; But you can't setting the spawn in other dimensions (You will encounter an overwhelming military groups of a warzone hellscape in other dimensions ; espacially the dimension was very dark or "desert-based" dimensions)

Should making a small config option to disable NPC spawning in certain dimensions to prevent this issue occur...

Also an option to whitelist other dimensions for the structures to spawn in. I would like to disable them in the overworld, but allow another dimension to spawn them.

Until there is an option I have used McJty's incontrol mod to handle this - you can disable spawns in any dimension / biome conditionally. Attached is the incontrol spawn.json file I am using right now - it prevents spawns in places like the twilight forest, aether and betweenlands where they just don't make sense.
spawn.zip

Posting this just to hopefully revive the discussion on this. I am currently making a modpack where I want a dimension that isn't the overworld to have had a "zombie outbreak" and use techguns structures and enemies to portray that. Being able to choose what dimensions the techguns structures and mobs spawn in would be an awesome addition

Until there is an option I have used McJty's incontrol mod to handle this - you can disable spawns in any dimension / biome conditionally. Attached is the incontrol spawn.json file I am using right now - it prevents spawns in places like the twilight forest, aether and betweenlands where they just don't make sense.
spawn.zip

Thanks @psilver2001 ! This really helped. Biome blacklist doesn't really work good with mods like Advent of Ascension that add 20+ dimensions with multiple biomes and there is no list of biomes online. Can't wait for dimension blacklist option. :D