Disabled Root Login by mistake

As understood, you haven't configured the root account. It should still use defaults then, therefore, give a try to steps below.

Log in via SSH with

root/default

, proceed to restore the config before your last change with

cp /config/bigip.conf.bak /config/bigip.conf

followed by

tmsh load sys config

commands. In the future, if you run into issues, check the /var/log/ltm file. It reports most of the problems very accurately.

Also note that you cannot actually disable the root account, its part of RHEL, not F5 TMOS config. Regardless of the auth scheme you choose (TACACS, RADIUS), the undeletable account named root always uses on-appliance authentication method. The account is linked to the Linux system underneath F5, and you would have to try hard to make the root account not work 🙂