I tried to look up total conversion and other mods as examples (Counter-Strike, Defense of the Ancients, Gunman Chronicles, Dear Esther, Natural Selection) but it is a bit difficult to find out if they (and other total conversion mods) required a little or a lot of programming.
I ask this out of pure curiosity, as I have heard some people claim you can make a total conversion with absolutely no programming skills. However, this is not easy to research as google does not bring up articles mentioning how total conversion mods do/don't require programming skills.