A: The Goal change and the Larry move are considered to be simultaneous, so we would rule that Larry/Potato blocks that win.
If the only thing preventing your meeting the Goal for the win is Larry or the Radioactive Potato, and playing the Goal causes them to move AWAY from you, you’re fine. If playing the Goal makes them move ONTO you, then you’re stuck. No win. Getting timing right to play the Goal you need is part of the challenge of having either of these on the table.