Are these firewalls plus management servers, or just firewalls?
If they are just firewalls, do you have access to the command line of the management server which manages them?
If so, you may be able to use this to run commands on the firewall:
cprid_util -verbose -server "<firewall address>" rexec -rcmd <some command here>
Replace <firewall address> with the main IP address of the cluster member where you want to run the command. For example, this would add a new administrative user to a firewall (or cluster member) with the main IP 10.20.30.40:
cprid_util -verbose -server "10.20.30.40" rexec -rcmd clish -s -c "add user someNewUser uid 0 homedir /home/someNewUser"
If the returned data includes "(NULL BUF)", that means the management couldn't connect to CPRID on the firewall or member.