Isabelle,

I'm using Excel 2007 SP2.

Sub Macro_Change_Function()
'
' Macro_Change_Function Macro
'

'
With Sheets("Data")
x = .Range("First_Data_Cell").Formula
y =
Application.Substitute(x, .Range("Current_Function"), .Range("Selected_Function"))
.Range("First_Data_Cell").Formula = y
End With
Application.Goto Reference:="First_Data_Cell"
Range(Selection, Selection.End(xlToRight)).Select
Selection.FillRight
Selection.SpecialCells(xlCellTypeLastCell).Select
Selection.FillDown
End Sub

Changes I made:

1) Changed the worksheet name from Sheet1 to Data

2) Changed the name "First_Cell" to "First_Data_Cell"

3) Added VBA code for filling right and down



- Ronald K