Sorry, forgot to get back to this one.
The new terminology is confusing, you have a Relationship Type, a SnapMirror Policy Type and a SnapMirror Policy. It takes a while to get a hang of the concepts especially as the manuals don't really do a great job of explaining things.
I did resolve it more or less along the lines that you suggested.
- Modified the existing relationship to SnapMirror policy XDPDefault
- Completed a SnapMirror update specifying one of the older snapshots
- Modified the SnapMirror policy back to MirrorAllSnapshots
- A subsequent snapmirror update relciated all the older snapshots
Thanks,
Ty