Thanks for the clarifications. I don’t even know this Nix / Flake well enough to understand the difference between with or without Flake. Might be worthwhile techniques for me to look into some day.
For now I will skip it and focus on Allow customising name of DeltaChat folder - #9 by Simon . I will definitely not be able to implement any user interface changes, but I can try to build 2 versions of the Android app (thanks to this easy Flake / Nix environment 
) to have hard-coded folder names for me and my wife, such we can test the use case of single mailbox multiple users, at least on Android.