a B&M casino, changing seats (not tables: seats)
is relatively simple. You tell the dealer you want
a seat change and (assuming you're first on the seat
change list) as soon as a seat opens up, you're given
the option to take it. If you pass on the open seat
because you only want to move to one of a few special
seats, you normally don't lose your place in line
on the seat change list as long as you tell the dealer
you want to keep it.
Online, changing seats is a bit more problematic.
You cannot change seats unless a seat opens and there
is no waiting list. This lets you leave the game and
then return, buying in as if you were a new player.
This has its risks; others could jump in and claim
the empty seats in the few seconds you're away.