You're correct, just remember to shut down your VM before taking the new snapshot.
No changes to the pool settings are needed, but you will need to recompose and point to the new snapshot.
I`m also thinking about using new pool as only a few people need more RAM.
In this case, can I clone existing parent machine? but then the snapshot would be consolidated.
Or I have create new parent image, bring image to same level as old parent VM ?
You can clone the original image without any issues (you could even use the same parent, pointing to different snapshots as the vm config is also part of the snapshot, but that could make it harder for other admins to understand).