There is nothing wrong with "cutting" a stock spring. As long as you don't use excessive heat to make the cut, it will be just fine. One coil equates to about a 2" drop but that depends on the condition of your springs.
What you never want to do is "heat "springs to get a drop. That will destroy the tempering and eventually the springs will sag, collapse, or even crack. Here is a heated spring, and a cut spring so you can see the difference.