How to programatically add folder to Spotlight "do not index"? Is there any way to programmatically add a folder to Spotlight's "Privacy" tab?
Either through Terminal or Applescript?

Often I want to click on an item in Spotlight results in Finder, and have that item's folder no longer be indexed.

I found that if you 

sudo defaults read /Volumes/foo/.Spotlight-V100/VolumeConfiguration.plist Exclusions


you can see an array with all the items excluded.

But if you try to 

sudo defaults write  /Volumes/foo/.Spotlight-V100/VolumeConfiguration.plist Exclusions -array-add '/path/to/folder' 


it does NOT get added to the Privacy tab in the Spotlight Preference Panel, nor does it get de-indexed.
According to an answer here, a folder can be excluded from Spotlight indexing (achieving the same effect as adding it to the Privacy tab, although the folder won't actually be listed there) by either


adding .noindex to the end of the folder's name, or
creating an empty file .metadata_never_index inside the folder (eg with touch folder/.metadata_never_index)


You will need to restart Finder after adding  .metadata_never_index, either killall Finder from Terminal or logout from the Apple menu and then log back in. This method doesn't work in Mojave and later.