past special....transpose....

Option Base 1
Sub Convertir_Les_Dates()
Dim c As Range, n As Byte
liste_mois_francais = Array("/01/", "/02/", "/03/", "/04/", "/05/", "/06/", "/07/", "/08/", "/09/", "/10/", "/11/", "/12/")
liste_mois_anglais = Array("JAN", "FEB", "MAR", "APR", "MAY", "JUN", "JUL", "AUG", "SEPT", "OCT", "NOV", "DEC")
For Each c In Range("B2:B" & Cells(Rows.Count, 2).End(xlUp).Row)
  jour = Left(c, 2)
  mois = Mid(c, 3, 4)
  an = Right(c, 4)
  n = 0
  For Each m In liste_mois_francais
    n = n + 1
    If m = mois Then Exit For
  Next m
  mois = liste_mois_anglais(n)
  c.Value = jour & mois & an
Next
End Sub

Set plage = Range("B2:B" & Cells(Rows.Count, 2).End(xlUp).Row)
plage.NumberFormatLocal = "[$-409]jjmmmaaaa;@"

Sub test2()
Dim c As Range, plage As Range
Application.ScreenUpdating = False
Set c = Range("A2")
Set plage = Range("B2:B" & Cells(Rows.Count, 2).End(xlUp).Row)
plage.NumberFormatLocal = "[$-409]jjmmmaaaa;@"
Do While c(2, 1) <> ""
  If c(2, 1) = c Then
    'If IsEmpty(Cells(c.Row, 3)) Then
    If Cells(c.Row, 256).End(xlToLeft)(1, 2).Column = 3 Then
      c.Offset(0, 1).Copy Cells(c.Row, 256).End(xlToLeft)(1, 2)
    End If
    c.Offset(1, 1).Copy Cells(c.Row, 256).End(xlToLeft)(1, 2)
    c(2, 1).EntireRow.Delete
  Else
    Set c = c(2, 1)
    c.Offset(0, 1).Copy Cells(c.Row, 256).End(xlToLeft)(1, 2)
  End If
Loop
Rows(1).Delete
Application.ScreenUpdating = True
End Sub

Sub Transposer()
Dim i As Long, j As Long, X As String
With Sheets("origin")
'ici on n'efface pas les données des colonnes A et B
'on transpose à partir de la colonne D
 X = .Range("A2"): .Range("D2") = X
  For i = 2 To .Range("A65536").End(xlUp).Row
    If .Cells(i, 1) = X Then
      j = .Range("D65536").End(xlUp).Row
      If .Cells(j, 256).End(xlToLeft).Column = 4 Then
        .Cells(j, 256).End(xlToLeft).Offset(0, 1).Resize(1, 2) = .Cells(i, 2)
      Else
        .Cells(j, 256).End(xlToLeft).Offset(0, 1) = .Cells(i, 2)
      End If
    Else
      j = .Range("D65536").End(xlUp).Offset(1, 0).Row
      .Cells(j, 4) = .Cells(i, 1)
      If .Cells(j, 256).End(xlToLeft).Column = 4 Then
        .Cells(j, 256).End(xlToLeft).Offset(0, 1).Resize(1, 2) = .Cells(i, 2)
      Else
        .Cells(j, 256).End(xlToLeft).Offset(0, 1) = .Cells(i, 2)
      End If
      X = .Cells(i, 1)
    End If
  Next i
End With
End Sub