The following code will change all comments to Times New Roman, font
size 12:
'======================
Sub FormatAllComments()
Dim ws As Worksheet
Dim cmt As Comment
For Each ws In ActiveWorkbook.Worksheets
For Each cmt In ws.Comments
With cmt.Shape.TextFrame.Characters.Font
.Name = "Times New Roman"
.Size = 12
End With
Next cmt
Next ws
End Sub
'========================