If i reserve seat on Shinkansen from Tokyo to Kyoto but can not catch it - let’s say run late or decided to leave later after seat is booked. What would be my action? Can I reserve a seat for later train? Thanks!
Generally speaking, you should still be able to board a train even without a seat reservation - you will just be limited to the unreserved seating areas. As far as I know, you can also change your reservation by popping into the JR ticket office.