Thanks, and no, I have seen that topic and can not see how it is related. Remember I am making a docker image which needs to have these repositories inside it, I am not flashing anything. I am running jetson with the Jetpack sdcard image provided by nvidia, and inside it I have a docker image based on nvidia l4t image, which I want to customize, by adding these repositories to /etc/apt/sources.list.d/nvidia-l4t-apt-source.list as the original sdcard image has them.
I can manually edit this package and ignore the check it performs so it can be installed, my question is why the developer has assumed that this should not be done in this way, and as another question, where I can find the GPG key for these repositories.