Turn Audit Trail on and off

I am looking to only use the audit trail vba code when a command button is used. I have the following two options for audit trails - the first does not collect all of the information when used as a macro and the second gives an error for the target. Is it possible to selectively use code when it is assigned to a worksheet?

Dim vOldVal
'Must be at top of module

Private Sub Workbook_SheetChange(ByVal sh As Object, ByVal Target As Range)
Dim bBold As Boolean
If Target.Cells.Count > 1 Then Exit Sub
On Error Resume Next
    With Application
         .ScreenUpdating = False
         .EnableEvents = False
    End With
    If IsEmpty(vOldVal) Then vOldVal = "Empty Cell"
    bBold = Target.HasFormula
        With Sheets("Log")
            .Unprotect Password:=""
                If .Range("A1") = vbNullString Then
                   .Range("A1:E1") = Array("CELL CHANGED", "OLD VALUE", "NEW VALUE", "TIME OF CHANGE", "DATE OF CHANGE")
                End If
          With .Cells(.Rows.Count, 1).End(xlUp)(2, 1)
                  .Value = Target.Address
                  .Offset(0, 1) = vOldVal
                      With .Offset(0, 2)
                        If bBold = True Then
                          .ClearComments
                          .AddComment.Text Text:="OzGrid.com:" & Chr(10) & "" & Chr(10) & "Bold values are the results of formulas"
                        End If
                          .Value = Target
                          .Font.Bold = bBold
                     End With
                .Offset(0, 3) = Time
                .Offset(0, 4) = Date
            End With
            .Cells.Columns.AutoFit
            .Protect Password:=""
        End With
    vOldVal = vbNullString
    With Application
         .ScreenUpdating = True
         .EnableEvents = True
    End With
On Error GoTo 0
End Sub

Private Sub Workbook_SheetSelectionChange(ByVal sh As Object, ByVal Target As Range)
vOldVal = Target
End Sub

Here is the second one:

Dim PreviousValue

Private Sub Worksheet_Change(ByVal Target As Range)
    If Target.Value <> PreviousValue Then
        Sheets("log").Cells(65000, 1).End(xlUp).Offset(1, 0).Value = _
            Application.UserName & " changed cell " & Target.Address _
            & " from " & PreviousValue & " to " & Target.Value & " at " & Time
    End If
End Sub

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
    PreviousValue = Target.Value
End Sub