…the above is the exact approach most developers use. There will be some default file elsewhere in the operating system. If you find
10periodic somewhere else, or
20auto-upgrades, and you wish to edit that content, then simply copy it to
/etc/apt/apt.conf.d/, and then edit there. Removing that file (or just disabling it by compressing it) will revert back to the original behavior. Putting the edited file back in place will produce the modified behavior.
You could also just create the file as you want. I don’t know how to test if this is set, but for example I have:
…and the content of that file is:
Thus my system will update the package list, but won’t actually upgrade anything. I get to see a message about how many packages need update, but I pick which packages to upgrade, and when to do so. I suggest just put the file in place and see if it works how you want.