In software sources I have two entries that say Added by software-center; credentials stored in /etc/apt/auth.conf. I can see on the URIs that they are sources for software I have bought (for 0 $) in the Software Center, and removed again. Now I have a lot of sources, as I experiment with some PPAs, so updating them ís not as fast anymore, so I would like to know if I can safely remove these entries, and still be able to install the software again later?
When I asked this question, I was afraid something weird would happen if I deleted the sources, that would require bothersome manual fixing and stuff. Later I tried to add a PPA from command line twice, and got garbage lines in the corresponding .list file (located in /etc/apt/sources.list.d/), and I imagined something similar could happen with the sources added automatically when you buy software from the software centre, having disabled or deleted the source. Now I'm (mostly) done with my exams, and have found time to experiment with this myself.
The result of installing bought software again, after having removed it, and disabled the source, is that it just creates an identical source upon installing the software again (The identical source of course being enabled, contrary to the one that was already there). Upon this I drew the following conclusion:
It is safe to remove software sources for software bought in the software centre completely.
I double checked this by removing (instead of just disabling) the two sources I had (one enabled, and one disabled) after my second installation of some software I bought previously, and then installed it again. Worked flawlessly.
I tested this with both 0$ and > 0$ software in the Software Centre.
Removing unused repos should be ok, but I don't know if the software will stll be free if you decide to reinstall it later.