Mass way to modify number values

Select each sheet containing the numbers that you wish to adjust and run this small macro:

Sub AdjustNumbers()
    Dim rAdjust As Range, r As Range
    Set rAdjust = ActiveSheet.UsedRange.Cells.SpecialCells(xlCellTypeConstants, xlNumbers)
    For Each r In rAdjust
        r.Value = r.Value * (100 + Application.WorksheetFunction.RandBetween(-20, 20)) / 100
    Next
End Sub