Yes you can. There is no rule against it (unless it's been sneaked in very recently since I last looked) and I can't imagine any TPE Guard turning down your money (assuming seats are available of course)Can you upgrade to 1st Class with a STD advance on TPE? I've read somewhere you can, but then when asking the question on the official twitter, i was told it's not possible.
Yes you can. There is no rule against it (unless it's been sneaked in very recently since I last looked) and I can't imagine any TPE Guard turning down your money (assuming seats are available of course)