For example, to add the `non-free` sections of Debian 13 (Trixie), backports, and security updates, you can create a file named */live/persistence/TailsData_unlocked/apt-sources.list.d/non-free.list* with the following content:
Correct the ownership and permissions of your additional `sources.list` files to be owned by `root` and only readable by others. For example, execute the following commands.