They have not been, which is why I suggested it. It’s in my to-do but if someone wants to do that before me they can.
Good questions!
I think originally the only variable that could be set was $KDEHOME and the system paths were built in.
It could still be that the code uses the built-in default for $XDG_CONFIG_DIRS when evaluating kiosk rules, however that would need to be checked.