It is, but do you have to do it before the formula is committed to the sheet?
You could examine the formula directly after committing it to the sheet using a Worksheet_Change event. This in the sheet concerned's code-module:
Code:
Private Sub Worksheet_Change(ByVal Target As Range)
myString = Target.Formula
MsgBox myString
If UCase(Left(myString, 5)) = "=SUM(" Then
strRng = Split(Split(myString, "(")(1), ")")(0)
MsgBox strRng
End If
End Sub
Not very robust but with a few more IFs perhaps could be made to do what you want.