Sub MiseEnForme()
Dim xRg As Range, Vals, i As Long
Set xRg = Range(Cells(2, "a"), Cells(Rows.Count, "a").End(xlUp))
Vals = xRg.Value
For i = 1 To xRg.Rows.Count
On Error Resume Next
Vals(i, 1) = Format(Split(Vals(i, 1), "/")(0), "00000000") & Format(Split(Vals(i, 1), "/")(1), """/""00000")
Next i
On Error GoTo 0
xRg.Value = Vals
End Sub