Sub insere()
For col = 1 To Cells(1, Columns.Count).End(xlToLeft).Column
If InStr(Cells(1, col), " ") = 0 Then ' pour eviter des ennuis si la macro est répetée
a = Mid(Cells(1, col), 1, 4)
b = Mid(Cells(1, col), 5, 3)
c = Mid(Cells(1, col), 8)
Cells(1, col) = a & " " & b & " " & c
End If
Next
End Sub