[assbuttbuttass]

I'm not sure where you got that XDG_DATA_HOME has to be read-only, I couldn't find anything like that

> $XDG_DATA_HOME defines the base directory relative to which user-specific data files should be stored.

And really, the difference between XDG_DATA_HOME and XDG_CONFIG_HOME is subjective anyway, each application will have its own requirements, so I'm not convinced it's even possible to define these completely precisely.

Personally, I would pick between XDG_DATA_HOME vs XDG_CONFIG_HOME based on whether the application manages the files, or whether the user is expected to manage the files themself. This isn't based on any wording in the standard, but just a pattern I've commonly seen