Private Sub Worksheet_Change(ByVal Target As Range)
'La colonne A doit être au format Texte
Set Target = Intersect(Target, Range("A2:A" & Range("A" & Rows.Count).End(xlUp).Row + 1), UsedRange)
If Target Is Nothing Then Exit Sub
Dim dat As Variant
Application.EnableEvents = False 'désactive les évènements
For Each Target In Target 'si entrées multiples (copier-collage spécial valeurs)
dat = IIf(Target Like "########", Format(Target, "00\/00\/0000"), "")
If IsDate(dat) Then Target = Format(dat, "dd/mm/yyyy") Else Target = Empty
Next Target
Application.EnableEvents = True 'réactive les évènements
End Sub