ghostrider

I change mine frequently with no ill effects when I change it back. I use many different types of thread, but also some pretty unusual "fabrics" (like paper, foils, metals, etc) so changing the bobbin tension is a necessity in some cases.

I simply made a mark on the bobbin case with a fine point Sharpie that lined up with the slot of the screw before I moved it for the first time. Now I can set it back again with no fear. There's lots of info on changing bobbin tension available online. More and more people are "daring" to do it these days.

Suggestions: take baby steps in the turning, use the face of a clock as reference points, make notes on what position works best for what combo of threads and fabric so you'll know for next time.