New PS6210 use first and add to pool later

Good afternoon All

I have a 2 unit SAN (PS6210  x 2) and I now have a new 3rd PS6210 - part of my problem is that the Firmware versions are 2 versions different so I can add the new one into the existing pool.  The 2 unit pool is almost full and it would mean quite a lot of disruption to upgrade the firmware straight away.   Is it possible for me to add the new unit as an independent pool, move some of my VMs to it then upgrade the 2 units and then add the new unit into the old pool?  Or would the adding destroy the data on the new pool?

Thanks

Eric