You can specify as many profiles as you want, you have a property called firefox.profiles that can be an array and you would declare as many settings you would want in it. They still need to be names though (either through a variable like an username or a name you would set yourself).

It’s increasine in complexity when you are writing shell scripts, it is not when you have a proper system in place that provides a sane abstraction/interface for defining such configurations.

Guix is a huge upfront increase of complexity for someone who already has a shell script to do the same thing.