Say 2 of 4 crewmembers going up in a Dragon are set to ramain on ISS for
one year.

This means they come up on one Dragon, and come back on another Dragon
that launched 6 months later, midway into their mission.

When the second Dragon arrives, what does the "official" switch involve
for those 2 crewmembers? Just moving their launch/entry suits from the
old Dragon to the new one which becomes their lifeboat for second half
of mission? Or are there seat liners as well?

If there are no liners like on Soyuz, would the seats require various
adjustments to size of seat, leg rest etc ? or are they pretty must one
size fits all?

JF Mezei presented the following explanation :
> Say 2 of 4 crewmembers going up in a Dragon are set to ramain on ISS for
> one year.
>
> This means they come up on one Dragon, and come back on another Dragon
> that launched 6 months later, midway into their mission.
>
> When the second Dragon arrives, what does the "official" switch involve
> for those 2 crewmembers? Just moving their launch/entry suits from the
> old Dragon to the new one which becomes their lifeboat for second half
> of mission? Or are there seat liners as well?
>
> If there are no liners like on Soyuz, would the seats require various
> adjustments to size of seat, leg rest etc ? or are they pretty must one
> size fits all?

It's easier to get details on the suits than the seats, but there is
some out there:

"The seven seats mount to strong, lightweight supporting structures
attached to the pressure vessel walls. Each seat can hold an adult up
to 1.95 meters tall (6 feet 5 inches) and weighing 113 kg (250 lbs),
and has a liner that is custom-fit for each crewmember."
<URL:https://phys.org/news/2012-03-spacexs-dragon-seating.html>

Yes, that's 2012, but that seems to be current information still. Oh,
and I'd fit.

"The seats in the Crew Dragon spacecraft are reconfigurable, allowing
it to carry up to seven people—though four is typical for a NASA
mission. Three large touchscreens replace the traditional instrument
panel. Courtesy SpaceX"
Caption for 2nd picture at
<URL:https://time.com/6083975/inside-spacex-crew-dragon-spacecraft/>

SpaceX's ewtewbs include a tour in the 4-seat configuration, no cargo
stowed below as is common in flight.
<URL:https://youtu.be/78ATfCaBn6E>

Tech-Crunch has a link to the SpaceX video of the suit plantation:
<URL:https://techcrunch.com/2020/07/28/spacex-offers-an-inside-look-at-how-it-created-its-futuristic-dragon-space-suits/>

Phys.org seems to have an answer to your question, but how you move the
seatliners isn't revealed there.

/dps

--
"First thing in the morning, before I have coffee, I read the obits, If
I'm not in it, I'll have breakfast." -- Carl Reiner, to CBS News in
2015.