А если не "х", а что-то другое?
Сделал для любого значения. И для любого количества вставляемых значений
[vba]Код
Private Sub Worksheet_Change(ByVal Target As Range)
Dim d_ As Range, da_ As Range, d0_ As Range
r0_ = 2
r1_ = Cells(Rows.Count, 2).End(3).Row
Set da_ = Cells(r0_, 1).Resize(r1_ - r0_ + 1)
Set d_ = Intersect(Target, da_)
If Not d_ Is Nothing Then
Application.ScreenUpdating = 0
Application.EnableEvents = 0
For Each d0_ In d_
If d0_.Value <> "" Then 'If d0_.Value <> "x" Then
z_ = d0_
da_.ClearContents
d0_ = z_
Exit For
End If
Next d0_
Application.EnableEvents = 1
Application.ScreenUpdating = 1
End If
End Sub
[/vba]