Another way
Option Explicit
Sub DoStuff()
Dim pt As PivotTable
Dim ptTable As Range, rNeg As Range, rNegRow As Range
Dim i As Long
Set pt = ActiveSheet.PivotTables(1)
Set ptTable = pt.TableRange1
With ptTable
If pt.RowGrand Then Set ptTable = .Cells(1, 1).Resize(.Rows.Count, .Columns.Count - 1)
If pt.ColumnGrand Then Set ptTable = .Cells(1, 1).Resize(.Rows.Count - 1, .Columns.Count)
End With
With ptTable
.Cells(0, 1).Offset(1, .Columns.Count + 3).CurrentRegion.Clear
.Copy
.Cells(0, 1).Offset(1, .Columns.Count + 3).PasteSpecial Paste:=xlPasteValues
Set rNeg = .Cells(0, 1).Offset(1, .Columns.Count + 3).CurrentRegion
Set rNegRow = .Cells(0, 1).Offset(1, .Columns.Count + 3).End(xlDown).Offset(1, 0)
End With
Set rNeg = rNeg.Cells(2, 1).Resize(rNeg.Rows.Count - 1, rNeg.Columns.Count)
rNeg.Copy rNegRow
Set rNeg = rNeg.CurrentRegion
On Error Resume Next
For i = rNegRow.Row To rNeg.Cells(1, 1).End(xlDown).Row
ActiveSheet.Cells(i, 13).Value = -1 * ActiveSheet.Cells(i, 13).Value
Next i
On Error GoTo 0
End Sub