Disable magnetic screen on/off *without* Xposed?
You can delete /dev/input/event6 directly. Then everything with the Hall sensor will stop working.

To make this happen automatically, you can write a simple script and let it auto-run at boot.

#!/system/bin/sh
exec rm -f /dev/input/event6


To restore without rebooting, examine it with ls -l before deleting (or you have to reboot)

Assume ls -l gave this result:

crw-rw---- root input 13, 68 1970-01-01 00:00 /dev/input/event6


Take note of the two numbers after owner/group, run this to recover

mknod /dev/input/event6 c 13 68