أولا السلام عليكم ورحمة الله 
لى طلب بشرح هذا الكود 
 
Private Sub Worksheet_Change(ByVal Target As Range)
On Error Resume Next
If Me.[T1] Then Exit Sub
    If Not Application.Intersect(Target, Range("myrange")) Is Nothing Then
	    Application.EnableEvents = False
	    Application.Undo
	    Application.EnableEvents = True
    End If
End Sub
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
On Error Resume Next
    Dim Rng As Range
    Static Cell As Range
    Static TheFormula As String
    Set Rng = Range("myrange")
    If Not Application.Intersect(Target, Rng) Is Nothing Then
	    If Not Cell Is Nothing Then
		    Cell.Formula = TheFormula
	    End If
	    Set Cell = ActiveCell
	    With Cell
		    TheFormula = .Formula
		    .Value = .Value
	    End With
    Else
	    With Cell
		    .Formula = TheFormula
	    End With
    End If
End Sub
باعتبار أن النطاق myrange نطاق محدد
ما هو المراد بـ 
If Me.[T1] Then Exit Sub