The seat liners can be installed in Soyuz on-orbit. When the Shuttle was delivering someone who would return on a Soyuz, they'd bring the liner up as cargo on t

The seat liners can be installed in Soyuz on-orbit. When the Shuttle was delivering someone who would return on a Soyuz, they'd bring the liner up as cargo on the Shuttle and swap it in. I imagine they routinely do the same for crew who arrive and depart on different Sayuz (which happens fairly regularly.)