Changing the second prompt. :{ modules| No setting available to change.
In order to change the main prompt it's as simple as a single command.
:set prompt "> "
However, in order to change the second prompt, you'd have to go into the ghci source code, and remove code or wrap existing code to add a switch/configuration for it.
Example..
> :{
Prelude|
As of the reason to having a configurable prompt, when you have many modules, this list can become annoying fast and so many have disabled showing the modules. Yet we can't do this with the second prompt.