I was flagging a couple of images as dupes and there was a mix up with one of the post IDs and I had no way to correct it.
I had to put a comment noting the correction on the post and hope it is noticed.
Being able to correct the flag itself would make life easier for the admin dealing with it.

better option when you make the flagging error, is to edit the post and replace the false parent post ID with the the actual ID