Change le nom de ton sheet et ta colonne
Sub test()
Dim NumSem As Byte
Dim i As Long
NumSem = DatePart("ww", Date, 2, 2)
With Sheets("Lenomdetonsheet")
For i = 1 To .Range("A" & .Rows.Count).End(xlUp).Row
If Len(.Range("A" & i)) < 6 Then
.Range("A" & i) = NumSem & "-" & .Range("A" & i)
End If
Next i
End With
End Sub