Свойство FormulaLocal позволяет установить значение формулы, не активируя диаграмму / серию
Sub NewChart()
Dim chart1 As Chart
Dim newformula As String
Dim SC As SeriesCollection
Dim mySeries As Series
Dim STR As String
Set chart1 = ActiveSheet.ChartObjects("Chart 1").Chart
Set SC = chart1.SeriesCollection
Set mySeries = SC.Item(1)
STR = SC.Item(1).Formula
mySeries.FormulaLocal = STR
Debug.Print TypeName(Selection)
End Sub