I have done this exact same thing several times. It's really not all that different than jacking up a car, and much less chance of it falling off the jack. Lowering is no different than raising it. Either way, cracks will appear, but remember that the house was originally level (usually), so you are just getting things back to normal. I still cant understand why the former owner of the OP's house raised it too high. It's not that hard to use a $10 level.
I should mention that I have been lifting a barn where much of the foundation collapsed. That's much more complex and could be dangerous. But I just raise it a little every few weeks, and as it raises, the wood goes back to it's original form. Eventually it will be back where it belongs, then I got to rebuild the foundation (thats the hard part). The only advantage of a barn is no plaster to crack.
Just keep in mind. Whether you are levelling a house, or lifting a barn back on its foundation, GO SLOW. The reason is that things need to flex. If you go too fast, things may break. If you drop a 100lb weight on a 2x4 bridged between 2 blocks, the 2x4 will probably break. But if you apply 100 lbs of pressure (such as standing on it), it will flex, but not break. Raise or lower a little at a time, and nothing will break (except the inevitable plaster cracks). There might be a plaster popout at one or two spots too. It's the price you pay to level a house.
I have a friend that moves and sets these pre-built homes. I have helped him a few times when he was short on help, and it amazes me how these homes are hauled down rough roads, tilted, shifted, bent and distorted until they are finally on their foundations. Yet, there is little damage, but always a few plaster cracks.... Once they are set, he has his crew patch the cracks and touch up the paint. Not really a big deal.....
Mark