Answer:
The type of edit to direct quotes which is inappropriate is the following one:
Correcting errors in the quote.
Explanation:
If it is a direct quote, it is supposed to be as genuine as possible, that is, the essence of what was said by that particular person must be kept, and that includes not only what was said, but also how it was said- errors and all.
Eg: Let's say you want to quote Joker (played by Heath Ledger in "The Dark Knight") and you write:
As said by Joker: "Why <u>are you</u> so serious?"
In the example above, the essence of the original quote was lost, since the omission of verb and subject (Why so serious?) was what gave the classic quote its mysterious charm. So, it is best to keep it the way it actually is:
As said by Joker: "Why so serious?"