>>A message can only be edited if it has not been replied to. Look in the footer of the message frame for a folder icon with a small curved arrow over the top right corner. It's tooltip says "update". The icon does not appear if the message can not be changed.
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>Yes, but by the time the click is done, a reply might be created thus the reply functionality won't be possible.

Excellent point. The status can change after the icon is sent to your browser.