I've been wanting to do this! The plan was to modify the Bazzite DX version build script, but ultimately Fedora being base was a deal breaker for me. With KDE Linux this might finally be a dream come true.

It seems like KDE linux uses a different way to provide a system image than ostree on Fedora Silverblue, so I have no idea how easy it is to make changes on top of.

But for Bazzite (and other universal blue distros) you better use BlueBuild

https://blue-build.org/

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 !

https://github.com/LelouBil/Leloublue