How would you normally do it? Because you can still put redefinitions of all the standard functions into a single file and load them with `.` as you would with other shells.
Well I’m not suggesting the following is a better alt shell, but in murex you have something that’s a little bit akin to a Windows Registry in that all of the shell settings are navigable through a builtin called ‘config’
You can set prompt functions with that; strings, ints and Booleans too. And ‘config’ comes with descriptions for each configurable thing, choices of options in many cases, and an easy way to default back to shell defaults too. So it’s dead easy to play around configuring whatever you want (you never need to leave the shell to look up an option).
The shell has its own problems though but it’s an interesting alternative take for grouping shell config.
There's also this package, which the author admits only allows "slight" customization, to implement sessions: https://github.com/farzadghanei/fishion