Post 1 contains inappropriate content
Post 3 and 4 quote post 1, quoting the inappropriate content
Moderator edits post 1 and has to edit post 3 and 4 to remove all instances of the content.
With this tool, the moderator could edit post 1 and apply the changes in that post to all quotes (by clicking a button or something), just to save time.
I'm not sure about the overhead this could create, but I thought I'd suggest it anyway.