Back when I was young and naive and thought that ebay was a good place to buy supplies, I purchased a giant bag of these magnetic clasps to use in hand bags.
When said giant bag arrived, I realised that the magnet on them was way too strong and using them in my bags would risk ripping the lining when trying to open the bag. They sat in a magnetic and metal mass in a jar. They attraced each other from across my crafting table. It was almost impossible to separate them from each other much less from the male and female halves.
I found a work around and planted the magnetic clasps inside the lining so that there would be a piece of fabric between the two halves of the clasp. Problem solved.
But this process is somewhat time consuming and I didn't think it looked as neat as I wanted it to. So I started looking into how to weaken magnets on the world wide webs. I read that heat can weaken and even demagnetize magnets. I started experimenting with heating the magnets in both the oven and bowls of boiling water. After some testing, I found that the best way to weaken the clasps was to put them in the oven at about 300 or 350 degrees for a ten minutes or so. (I put them on a piece of foil to keep them from slipping through the wire rack and to make it easy to scoop them up. CAUTION: they are very hot when you take them out.) I completely demagnetized only one clasp during this experimentation process. They're still strong enough to clasp but not so strong that you have to dig a fingernail in between them to separate them. I'm in the process of putting some of my "new" magnets into bags, so I'll post here about how they turn out in real use. Thank you, Internets!!