I usually just copy the comment text to the clipboard, delete the comment and then create a new comment for the correct text.
The following macro automates this:
'assumes that the current selection contains just one comment!
Dim newrange As Range
Set newrange = Selection.Range
Selection.Comments(1).Range.Copy 'copy text of old comment
Selection.Comments.Add Range:=newrange 'create new comment
Selection.Paste 'add text to new comment
newrange.Comments(1).Delete 'delete old comment
I use the clipboard to be sure that formatting of the comment (such as different fonts) do not get lost, but I haven't tested if there is an easier way. The result is this:
Of course you might want to add some kind of error handling; if there is more than one comment in the selected region then it will take whatever Word considers to be the first one. Also, your new selection need to completely contain the old selection; otherwise
Selection.Comments is empty and