将VBA宏应用于多个单元

我会说我不是VBA专家。我有一个VBA代码，可以在一个单元格中附加来自选定列表的多个值。该代码有效，但现在我想将代码应用于多个单元格。

Option Explicit

Private Sub Worksheet_Change(ByVal Target As Range)
'Code by Sumit Bansal from https://trumpexcel.com
' To Select Multiple Items from a Drop Down List in Excel
Dim Oldvalue As String
Dim Newvalue As String
Application.EnableEvents = True
On Error GoTo Exitsub
If Target.Address = "$A$7" Then
  If Target.SpecialCells(xlCellTypeAllValidation) Is Nothing Then
    GoTo Exitsub
  Else: If Target.Value = "" Then GoTo Exitsub Else
    Application.EnableEvents = False
    Newvalue = Target.Value
    Application.Undo
    Oldvalue = Target.Value
      If Oldvalue = "" Then
        Target.Value = Newvalue
      Else
        If InStr(1, Oldvalue, Newvalue) = 0 Then
            Target.Value = Oldvalue & "," & Chr(10) & Newvalue
      Else:
        Target.Value = Oldvalue
      End If
    End If
  End If
End If
Application.EnableEvents = True
Exitsub:
Application.EnableEvents = True
End Sub

如何扩展代码以使用单元格范围

$A$7:$A$18 

而不是"$A$7"这样，以便我可以将VBA代码应用于Excel中的多个单元格。