Private Sub Worksheet_Change(ByVal Target As Range)
If Not Intersect(Target, Range("l13")) Is Nothing Then
    Application.Run Cells(13, 12).Value
End If
End Sub

Private Sub Worksheet_Activate()
    Dim oVBComponent As Object
    Dim strList$: strList = ""
    For Each oVBComponent In ActiveWorkbook.VBProject.VBComponents
        With oVBComponent
            If .Type = 1 Then
                With oVBComponent.CodeModule
                    For i = 1 To .CountOfLines
                        If InStr(1, .Lines(i, 1), "Sub ") And InStr(1, .Lines(i, 1), "Exit ") = 0 Then
                            strList = strList & ", " & Replace(Replace(.Lines(i, 1), "Sub ", ""), "()", "")
                        End If
                    Next i
                End With
            End If
        End With
    Next
    Set oVBComponent = Nothing
    strList = Mid(strList, 3)
    With Range("l13").Validation
        .Delete
        .Add Type:=xlValidateList, AlertStyle:=xlValidAlertStop, Operator:= _
        xlBetween, Formula1:=strList
    End With
End Sub