Installing zfsboot on FreeBSD 11.0

[Grzegorz Junka]

In the description of the loader

https://www.freebsd.org/cgi/man.cgi?query=zfsboot&sektion=8

we can read that if the drive is currently in use, the GEOM safety will 
prevent writes and must be disabled before running the above commands:

        sysctl kern.geom.debugflags=0x10

This worked fine on 10.3, but doesn't seem to work on FreeBSD 11.0:

root at crayon2:~ # sysctl kern.geom.debugflags=0x10
kern.geom.debugflags: 16 -> 16
root at crayon2:~ # dd if=/boot/zfsboot of=/dev/ada0s1a skip=1 seek=1024
dd: /dev/ada0s1a: Operation not permitted

Any suggestions?