banner is part of
dynconfig, it can be changed during runtime when
dynconfig is used
/confdConfig/runtimeReconfiguration` in the ConfD User Guide.
Then you can configure it directly (set
confdConfig cli banner "my banner" +
commit) or create e.g.
clispec custom command, that changes
Similar example how to change prompt is in
confdconf/dyncfg example directory.