I feel it would reduce the goals u concede from corner kicks.
My guess is that the training you do before a match doesn't impact anything but the bonus and players skills. So, by my guess, it wouldn't help you
About the offside trap, in real football theories it's useful against teams that tries to infiltrate your defense through the middle.
So if you move your defense line forward, the opponent would have more chances to be catch offside when attacking through the middle.
But if you move your defense line forward and your opponent is trying to get to the corner line and cross the ball, you should be in trouble. Dunno how it's programmed here in Top11, but I only use offside trap when it's clear for me that the opponent will attack through the middle