I am thinking of booking a tour in Japan. The tour includes a 7 day pass. But I would like to travel a bit after the tour. As the travel agency does not want to change the 7 day pass in a 14 day pass, I would have to buy a second voucher for a 7 day pass and change that for a new JR pass after the tour. Is it a problem to use the JR pass system two times in a row?