What Tiens are they?
If they are hight adjustable then the mounting cup on the bottom of the coilover should be able to be wound up or down. Raising or lowering the car.
If you are refering to the spring preload where by you compress the spring (between the top mount and the lower coil mount), effectively shortening it, you will lower the car but also increase spring rate, stiffing up the ride.
Dont "lower" the coils.
I haven't heard of what or how they do this but it sounds like chopping the springs, compressing them etc. All of which you dont want to do and will increase the stiffness.
If your going to do it, to it right from the start and the ride quality will be much better and it will handle better. Go to a spring company and order a set of springs in the right length, inner diamater and spring rate that you want.
You can usually pick up a pair of springs in your chosen height and spring rate for about $75-$100 each for something decent. Of course you can always spend more for better quality.