Folder action to append to Spotlight comment for files in Finder
I think I may have found the answer... 

on adding folder items to this_folder after receiving added_items

    tell application "Finder"

        repeat with currentFile in added_items

            set TheComment to the comment of the currentFile

            set comment of the currentFile to TheComment &amp; "test"

        end repeat

    end tell

end adding folder items to