You can put AlNiCo3 magnet in it. I did it, and it's somehow magical to me. Another nice option is AlNiCo 4.
AlNiCo 8 is a total overkill, AlNiCo 5 is all about boominess. Some people will recommend UOA5, but I didn;t ike it.
Microphonic feedback isn't a big issue with Seths, unless you are playing with tons of gain, with tube amp over 50W in a medium room. Otherwise you should be good. The feedback of Seths is very musical and controllable, and might come in handy if you leanr to use it properly.
EDIT: Found my old thread about magnet swapping in Seths, hope you find there what you are looking for
https://forum.seymourduncan.com/showthread.php?247913-Seth-Lover-Magnet-Swap&p=3446118&viewfull=1#post3446118