The basic rule for working on hot electronics is keep one hand "in your pocket", meaning don't have both hands touching the machine. That way if you touch high voltage, you may get a painful shock, but the current won't travel through your heart and kill you. That said, I've screwed up my courage and reached in with one hand and adjusted yokes, magnets, and the like on many CRTs, and have yet to be bitten. Be careful, and there's little chance of getting zapped. Working on tube hi-fi amplifiers is a lot more dangerous IMHO. 8-o

BTW, the yoke doesn't carry high voltage, so it's safe to touch the coils if you have to to break it loose. Or since you know you're going to rotate it anyway, loosen the clamp and give it a little turn before you turn the computer on. That way it'll be easy to turn when it's running.