Louvre time-stamped tickets; change time?

This is from the Official tickets website: The ticket purchased online is time-stamped and nominative, an identity document may be demanded. It is valid only for the chosen service, date and time. It is not a queue jump but gives access to the pyramid within half an hour of the time shown on the ticket. If the holder of the print@home ticket does not arrive within the allocated time slot for admission to the pyramid, they are subject to the same admission and waiting conditions as visitors without tickets.

You might try stopping by the ticket window to exchange tickets, but I would not bet on that either.

Note that admission to the pyramid is not admission to the museum; admission to the museum occurs at the wing of the museum and one ticket may be used throughout the day. So I read that to mean you don't get line priority at the pyramid i.e. admission within a half hour of your ticketed time, but you can queue and enter the lobby of the museum and then use that ticket regardless of time to actually enter the museum. Since people can come and go from the museum all day with one ticket, that is the only interpretation that makes sense. i.e. you get no more priority than an unticketed person AT THE PYRAMID, but otherwise the ticket just acts as an ordinary ticket.