by moving the links between the arms, he means that you can detach the clamshell link on the bar (the black rectangle), and position it so the endlink runs between the arms on the suspension's lateral link. the bar isn't really designed to be used that way and having it that stiff might get you into trouble on the street, but it's apparently the way to go for autoX.
it can on some cars*, but it also helps the car turn in a lot faster. depends on what you're looking for. with the 21.5 bar in the rear, a bigger front bar will probably not introduce any understeer problems. you'll probably appreciate the quick turn-in response more than the slight tail-happiness at the limit anyway.
(in reality, if you're understeering a protege on the street, you need to slow down.)
*some FWD cars, like the neon, understeer less w/ a bigger front bar.