I was the Tournament Director at our local Pub games and had to keep records of the players score board, put out the tables and chips every week, and generally make all the decisions when there were disputes, One of my jobs was to condense the tables when it was appropriate and switch players around.
Generally it was easy with only 2 or 3 tables going, keeping them balanced by moving the player on the next big blind, that way he might gain a spot or two on another table but still be eligible to post when his turn came, after all moving a player who had already posted the BB on one table, might have to Post it again on another table, and that would be unfair.
So the rule was the SB and BB were safe from being moved and stayed at their seats, and the player who was UTG moved to another table,