If your AP's get IP via DHCP then factory defaulting them should still allow them to be remotely accessed as long as the lease time is long enough. Before factory defaulting they should be reachable via CLI/SSH remotely via the configured IP address.
If the AP's are still connected to the SZ you could use the AP CLI script tool to set up the AP firmware. You would need to upload the AP firmware to a TFTP or FTP server and then send the update commands to run on the AP's in a Zone.
These are the commands to upgrade an AP via CLI which can be written into a Ruckus AP CLI script run per AP zone in an AP. Optionally you could create a script to do this from a linux server
fw set proto <(tftp or ftp)>
fw set host
fw set user (ftp only)
fw set password (ftp only)
fw set control fw up (This command initiates the update)
Details of creating AP CLI script:
SCG - AP CLI scripts
Execute AP CLI commands (for configuration options not available in SCG) into all the APs assigned to a zone
The set factory command will need to be run remotely on each AP and either DHCP option 43 with subcode 3 could be used for the AP's to discover the IP of the ZD's (unless the AP's are in the same IP subnet/VLAN in which case they can connect automatically) or you would need to access each AP and run set director ip . Unfortunately the firmware flash above should leave the AP's disconnected from the SZ so using a CLI script will not work.
I suggest testing this on one AP first to make sure it works and you understand the commands.
I hope this helps