Private Sub CommandButton1_Click()
Dim ligne
Application.ScreenUpdating False
For Each ligne In Range(Range('B65536').End(xlUp).Offset(1, 0), Range('A65536').End(xlUp).Offset(1, 0)).Rows
Range('B' & ligne.Row).FormulaR1C1 = '=IF(RC[-1]='''','''',REPLACE(RC[-1],1,1,''T)''))'
Next
Application.ScreenUpdating True
End Sub