Good question: the reply below is corrrct. Build time.

This is the way. Prototype in a regular distro then lock it in with an immutable distro.

I did exactly this with my XMonad/polybar/rofi/dunst/alacritty configs which I now run on NixOS.

You have to be trolling.

You actually CAN tinker with atomic distros even more.

Immutable distros offer penalty-free tinkering because of the aforementioned atomicity and rollbacks. If I screw something up, I can just rollback the entire OS or whichever parts I want.

Here’s another technology aimed at a similar idea: https://privtracker.com/