Hello Stephen,
I'm pretty sure I saw something written by Steven Beam somewhere which I used, but can't remember where.
Anyway, this is an extract of one of my WFA commands which should indicate how it works:
$VOLquery = Get-NcVol -Template
Initialize-NcObjectProperty -Object $VOLquery -Name VolumeIdAttributes
$VOLquery.VolumeIdAttributes.OwningVserverName = $VserverName
$VOLattrs = Get-NcVol -Template
Initialize-NcObjectProperty -Object $VOLattrs -Name VolumeSnapshotAttributes
$VOLquery.VolumeIdAttributes.Name = $VolName
$VOLattrs.VolumeSnapshotAttributes.SnapshotPolicy = $SnapshotPolicy
Update-NcVol -Query $VOLquery -Attributes $VOLattrs
Hope it helps.
Cheers!