edit and load bigip_base.conf

I´m a bit late to the party, sorry.

As far as I understand, your approach to modify these parameters directly in the configuration file is not supported by F5.

The command

tmsh load sys config

should load the configuration files indeed.

But as there is a potential conflicting information with the current configuration, it will not be applied. Instead you run the risk of an inconsistent configuration (text configuration files and binary configuration files).

Details on the subject can be found on AskF5 SOL13030. Reboot required ...

Please keep in mind, that a change on self IPs may break your device group setup. Putting one unit in 'forced offline' mode will prevent a potential active / active state.