Option Explicit
Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range)
If Range("i3").Value = "PREVISIONNEL DU" Then
If MsgBox(Prompt:="Etes-vous sûr ?", Title:="Attention !", Buttons:=vbYesNo) = vbYes Then
Exit Sub
Else
Range("i3:k3").ClearContents
End If
End If
End Sub