last time i organized at MIMUW the computers were named in a schematic way (room number based), wouldn't it be better to keep the computer name in?

Computers have their own names, but on some contests in WMI there are two different naming conventions. First which corresponds to stickers on computers--those are permanent and pretty much randomly permuted within each room and second printed and hung near the doors--they are ordered in a sensible way and change every so often. The former is useful for admins and is nearly useless and confusing for volunteers, while the latter is useful for participants and volunteers.
On the other hand I think that printing nice name instead of just id of a team/participant is better.

@kkmisiaszek while the tag feature (which i see is not removed in this PR) was invented for the purpose of creating groups (rooms most specifically), they could just as well be used to contain both numberings on the paper

i don't disagree with nice name for participant, but again, i don't think it has to be instead of id. again, i only have the experience of doing things the mimuw way, where iirc the computers for the olympiad have the participant id printed in large font on each desk

in general i would just advise that with the software being used in multiple environments the goal should be to make it useful for all of them instead of making haphazard changes or you'll incur the wrath of some city like we once did with kraków

What if

settings.PRINTOUT_HEADER_FORMAT.format(backup)

then you could configure any format you like in settings.py, eg:

PRINTOUT_HEADER_FORMAT = "Participant: {0.owner.nice_name} ({0.owner}) Computer: {0.owner.computer.nice_name}"