I recently contacted a luthier at a major guitar co. who asked not to be named for some info for my left handed blog. My question was: Can switching the strings around harm a guitar? Here is his answer:"We don't recommend anyone to switch strings, since bracing, bridges and tone bar are set up for right handed players. It is better to play it upside down. Otherwise it could be harmful to the structure of the guitar." Let me add that if you do this especially with an expensive acoustic and something breaks they probably wouldn't honor any kind of warranty that it might have. I'm not sure about solid body electrics but I do know that the bridge, saddle and nut would have to be adjusted. Ben