Solution 1:

I just found out how to expand or shrink the selected comment area without writing a macro or cutting/-copying/deleting the comment (In Word 10):

GO TO DRAFT VIEW. You will see your comment between 'handles' {red brackets} with the comment symbol on the side [in square brackets].

To expand/shrink the comment area, INSERT (cutting and pasting) THE NEW TEXT INSIDE the handles.

Example: the {N.Sea }[AB1] is cold today. Now move additional text inside the handle.

Example: the {N.Sea is cold }[AB1] today, this way you have expanded the comment area (if you move text out of it you will shrink it).

PS: the space before the } is necessary, it will not let you do this without it.

Hope it helps

Solution 2:

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:

Sub enlarge_comment()
 '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
End Sub

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:

screenshot showing before/after of the macro

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 Selection.Comments(1).Range.Copy fails.