Removing a coil or two from any spring will increase its compression rate, although not enough in your application, especially in the front where the spring acts on a lever at half the distance from the pivot to the wheel. Even in the back, where the rate is 1:1 with deflection, the rate will not increase sufficiently.
All springs act in a linear fashion, in other words if 100 pounds compresses it 1 inch, 200 pounds will compress it 2 inches, except for what are known as "rising rate" springs, which produce a slight improvement in rate with compression.
The fact is, if you want to lower the car you will have to increase the rate to prevent bottoming of the suspension. Years ago I purchased a set of IPD springs for my 142S and they were very impressive - transformed the car, along with a Volvo R-Sport front sway bar and wider tires. The springs were the single biggest improvement however.