I fix them using hot glue and test, so I can easily move them if they need to be adjusted. I don’t bother with the sticky pads that are supplied anymore.
Then when I’m happy with the position I peel off the hot glue and clean up with a bit of alcohol, then use high strength glue for a permanent bond.
I found those sticky pads or hot glue not good enough for long term use and the magnets fall of after a while.
If you have a hole in the magnet you can easily drill and tap an M3 thread into the lever, but that’s not necessary if you use decent glue.
Here is a photo of one of mine temporarily fixed on a tektro brake assembly with hot glue to get the position right.