We have 2 _new_ FAS8200's that need to be downgraded from ONTAP9.6 (which I believe comes as the OS) to ONTAP9.3P6 so:
the first FAS8200 can be added to a switched cluster and
the second can do a headswap ARL
I would like to speed up the process by dropping ONTAP9.3P6 onto the FAS8200 via the boot option 7 'install new software first' before any connections (shelves, network, etc.) are made so it boots to 9.3P6 after connecting it up. I know NetApp says "This menu option is only for installing a newer version of ONTAP software on a node that has no root volume installed. Do not use this menu option to upgrade ONTAP" but these have not been turned on yet and I was hoping to save a decent amount of time this way.
Older version may not be able to access disks used by newer version. So before directly installing 9.3, remove all aggregates, unpartition disks, if possible, zero spares (not sure if it works from maintenance mode) and unassign disks.
Once I observed old version crashed when booted on new firmware. I had to downgrade firmware as well.
So doing official revert is more fool proof, but requires working cluster and takes more time.