The seven volt mod is accomplished thusly,
the standard molex goes red (+5), black (ground), black (ground), orange (+12). Fans are typically hooked up to the hot orange and the ground black. For the 7v mod, you move the gound from black to red. Now you've got 12 pushing on one side and 5 pushing on the other. 12 wins by 7v. No, this won't hurt the PSU. What does it do to the 5v to the MB is another question. The fan probably drops the 7 volts, but the current will be higher than it would be otherwise. See as how the 5v lead is rated at 100X the current the fan is moving, it should be fine.