A simple, easy way of doing it is by using the amplify effect in audacity. Just select the audio and increase by a couple of dbs and listen to how it sounds (Remember to enable clipping). If you want it more distorted apply the effect again by different amounts until you get what you want.
Really what you are looking for is distortion. Any digital ...
Generally no. If the clipping was only one sample the CIA might be able to do it.
Clipping causes high order harmonics. Look at the FFT of a square wave versus a sine wave. The more you clip the more that sine wave looks like that bunch of squiggles from the square wave.