>The difference as I understand it is your Fish equivalent of a $PS1 (and other Fish shell behaviours) have to be defined via that path.
They don't. You have to define the function somehow, but fish doesn't care about how that happens. It's just that if it's not defined yet it'll try to load it from the file.
If you want, you can just do it all in config.fish, like you'd do it all in .bashrc for bash.
>what if you want to quickly change the prompt of a session without affecting other sessions?
Then you can redefine the function, just like you could switch the value of $PS1.
They don't. You have to define the function somehow, but fish doesn't care about how that happens. It's just that if it's not defined yet it'll try to load it from the file.
If you want, you can just do it all in config.fish, like you'd do it all in .bashrc for bash.
>what if you want to quickly change the prompt of a session without affecting other sessions?
Then you can redefine the function, just like you could switch the value of $PS1.