As we know that we are using Repositories for installing packages and repositories configuration file located at /etc/apt/sources.list.
I am using Ubuntu 12.10 (Quantal Quetzal) which reaches End of Life. That means no updates or support. So, the question is, can I use sources.list file from another version, say Ubuntu 12.04 LTS, and will it negatively affect the system.
Best Answer
12.10 is already beyond end of life.
But to answer your question, in general, unless you have a great deal of experience with apt, it is a bad idea to mix repositories. In your case, the packages in 12.04 are almost certainly going to be older then the packages in 12.10, and so it will do you no good.
In theory you can mix repositories using pinning, see https://help.ubuntu.com/community/PinningHowto
However, when pinning one generally installs a few packages.
In your situation, rather then mixing repositories, you would upgrade.
Because 13.04 is also at EOL I suggest a fresh install of 14.04. If you do not format your root partition, your data in
/homewill be preserved.