Can flatpak-builder copy a default config/data to user directories?

My application requires a configuration (ie. app.ini) and data file (app.dat).

I’d like to include a default configuration file but use $XDG_CONFIG_HOME. However, flatpak-builder seems to only allow copying to /app.

Is it possible to include default config/data files that are located in the XDG user directories by default?

no it is not possible.