oh i see.  So back to your original requirement. Using the same CG what's stopping your from creating a "dedicated" backup snapshot that will be used specifically for that purpose. Name is differently and manage it naviseccli.
We have been using our VNX with FC mounted LUNs for a Linux file server for a couple of years now.  We also have a VM which manages to keep 4 snapshots available in rotation for quick recovery during the day.  The LUNs were added to a snapshot consistency group.  We have a new requirement to keep a single snapshot open for backup to disk or tape, even if that takes a couple of days to complete.  This is to cover a worst-case scenario of losing the server and the VNX.  For this new backup process, can I create a second SCG with the same source LUNs?  I would like to keep the 4 daily rotation SCG unmodified if possible.  If not, can I create SnapView snaps alongside this SCG?  Let me know if this is not clear.
VNX Snaphots - Multiple CG or use SnapView