How can i edit a cell comment..?

try this:

For j = 2 To v + 1
' Sheets("Sheet1").Select
fault = Cells(j, 19).Value
Affecser = Cells(j, 15).Value
If Not Cells(j, col).Comment Is Nothing Then
    myStr = Cells(j, col).Comment.Text
    Cells(j, col).Comment.Delete
    Cells(j, col).AddComment.Text myStr & Chr(10) & fault & "(" & Affecser & ")"
End If
Next j

If a cell has a comment, the new text will be appended in a new line. If a cell does not have a comment, it will be skipped, i.e. no comment will be added.

cheers