So I can really separate the system-level changes (in the image, version-controlled) from my user changes.
It's a nixos-like experience without using nix at all.
There have been a couple of things to have in mind, with my Bazzite installation, for creating users or adding groups for example, this pointed me to use systemd-sysusers but it was simple.
But for Bazzite (and other universal blue distros) you better use BlueBuild
In the end it's an OCI container image, so you could technically just have a Dockerfile with "FROM bazzite:whatever" at the top, but bluebuild automates the small stuff that you need to do on top of it, and allows you to split your config in files.
You can have a look at my repository to see how easy it is !
The nice thing about Fedora Silverblue's model is that it is literally a container image, so to "build" your image you can run any arbitrary commands, so it's way simpler than nix.