Option Explicit
Private m_oFN As Footnote
Sub ScratchMacro()
  For Each m_oFN In ActiveDocument.Footnotes
    m_oFN.Range.Text = "(Note - " & fcnGetFootnoteReferenceIndex & ") " & m_oFN.Range.Text
  Next
lbl_Exit:
  Exit Sub
End Sub

Function fcnGetFootnoteReferenceIndex() As String
  With m_oFN
    With .Reference.Characters.First
      .Collapse
      .InsertCrossReference wdRefTypeFootnote, wdFootnoteNumberFormatted, m_oFN.Index
      fcnGetFootnoteReferenceIndex = .Characters.First.Fields(1).Result
      .Characters.Last.Fields(1).Delete
    End With
  End With
lbl_Exit:
  Exit Function
End Function