You either may edit a overlay (in /data/adb/modules/any-name/system/ or edit the file in filemanager of TWRP.Thank you, dear!
Nice, decent, people like you are always a pleasure to deal with, make up the heart of a welcoming community!
But I haven't: Magisk (20418) is dealing with my files in a manner that I cannot edit files in place. A question "Which file do I have to edit (in a Magisk 20418 environment) to make permanent changes to /a/b/c/d.xml ist clearly a Magisk-related question.
Have a great day, dear fried!
You may also flash your ROM again (dirty flashing should be enough).