This still works for El Capitan.
Instead of running sudo nvram boot-args="kext-dev-mode=1" you need to run sudo nvram boot-args="kext-dev-mode=1 rootless=0" , then install the modified kext. You can reenable the new rootless feature by running sudo nvram boot-args="kext-dev-mode=1" after you verified everything's working after a reboot.
Instead of running sudo nvram boot-args="kext-dev-mode=1" you need to run sudo nvram boot-args="kext-dev-mode=1 rootless=0" , then install the modified kext. You can reenable the new rootless feature by running sudo nvram boot-args="kext-dev-mode=1" after you verified everything's working after a reboot.