How to let custom meta data (boolean) change if certain tag exists (w Applescript)

You’re welcome!
You can have a unnecessary loop. Change your code to this…

tell application id "DNtp"
	if (selected records) is {} then return
	set tagMatchedFiles to (selected records whose (tags does not contain "xxx"))
	repeat with theRecord in tagMatchedFiles
		set md to false
		add custom meta data (md as boolean) for "yyy" to theRecord
		exit repeat
	end repeat
end tell