I have always down tuned to either drop d or E flat whenever I felt like it. The only thing was that I had a really cheap guitar that I didn't much care about. Now I have a much better guitar and I just wanted to make sure that down tuning isnt going to screw with the intonation or truss rod or anything. I definitely assume that it is OK considering I did it with my old guitar, I just wanted to be sure just to be safe. I most likely wont ever go lower that E Flat.