zfs(8) temporary mount point properties should include mountpoint
PROPERTY MOUNT OPTION atime atime/noatime exec exec/noexec readonly ro/rw setuid suid/nosuid In addition, these options can be set on a per-mount basis using the -o option, without affecting the property that is stored on disk. …
It seems peculiar to not find mountpoint in that shortlist.
There's altroot for zpool(8) but that does not allow for use cases where both:
a) the required pool is already is imported; and
b) it is inappropriate or undesirable to make a permanent (non-temporary) change to the mountpoint property value.