Nelson from Glouchester, Ontario made a jewelry box for his wife and put a magnetic catch on it. But the magnet works so well that he can hardly open the box. So he asked, "how do you weaken magnets?"
You can't actually weaken the magnet itself, but you can weaken its hold on the metal catch simply by not letting it come too close. Either move the magnet back so that it does not contact directly with the strike plate, or put one or two layers of duct tape or any more decorative tape on the strike plate to keep the magnet away. The magnet will still work, but the attraction will be weakened.