override zpool bootfs?

[goertzenator]

When booting with gptzfsboot, can I choose a root filesystem other than the one specified by the zpool's bootfs parameter?

I want to upgrade my gpt/zfs system by installing the latest FreeBSD to a new zfs filesystem, and then changing the bootfs param to boot it. If it doesn't boot, I would like to tell gptzfsboot to ignore the bootfs param use my old root filesystem.

I know I can use a livecd to change the bootfs parameter back, but I'll looking for something easier.

Thanks,
Dan.