Sen2Cor processing parameters

In order for atmospheric correction, a change in processing parameters is needed?

It depends on what requirements you have and where your image location is. For example, if you work with images in high mountains, it might be a good idea to switch terrain correction on.If your images cover a huge plain that would not be needed.

My personal experience for my study areas is that the default settings are enough. But I played a bit with the settings and read parameter descriptions before coming to that conclusion.