You'll need some sort of accepting system, otherwise people will just be stealing each other's seats and causing arguments.
And once you do that, you'll run into problems like "seats 0 and 2 can't switch because 1 and 3 are between them and don't want to switch"
switch 0 and 1, then 1 and 2, then 0 and 1 again
now it's a puzzle game!
What if you would "select" what seat you wanted to change to via next or previous seat (clientside feedback to which mount node, such as bottom print or center print), then hitting something like numpad 0 would attempt a jump to that seat? If the seat is occupied, you'd get a swap request, and if accepted, you'd swap seats.
Pressing numpad 0 when selected on your own seat would either do nothing or tell you what seat you're currently in.
Only issue is memorizing where on the vehicle your seat is, but you'd have that problem before you got on anyways.
Uh, what about we just do /seatswap _
Player's name_ and have the server sided script just check if you're in their vehicle, then just swap?
no arrow BS because you'd swap with every person currently riding. and would take forever if people don't notice the chat/client spam.
Not that hard folks.
Ninja: King of next page beeyotch