Those magnets would work fine, it's all a matter of what size you get. I'm afraid I don't remember what sizes I used myself...
I magnetized my Fex, as well as Warriors. The fex's legs are separate from the torso for transport, the head can be swapped out for Enhanced Senses, the back plate can be switched although I never do, and of course the arms for various weapon configs. It was not difficult to do, just make sure you put the magnets facing the right direction, and let the glue on each one dry before you do the next.
The warriors were more difficult because the magnets I used were much smaller, although plenty powerful. When they're so small they liked to rotate as I placed them in the holes I had drilled. My warriors have interchangeable heads for Enhanced Senses, and the weapon slots. Contemplating adding Extended Carapace options before I paint.
Magnetizing does add a fair amount of work, but if you want interchangeable parts it's the way to go. The downside is that you can't make as dynamic poses as you might like.