It is acceptable to cut springs, but remove no more than 1 inch from the overall length of the coil.
The rate for a coil spring is determined by the spring’s inside diameter (id), the number of active coils, and the wire diameter. To increase spring rate, use larger-diameter wire, a larger id, or fewer coils. but as soon as you cut a spring, the spring rate increases. This is due to a rule of coil-spring design that uses the number of coils and the wire diameter to determine the spring rate.
Also...The factory provides 2 rubber flanged cups that fit into both ends of the coil springs. These are sized to fit the tapered ends of the coil (once you take one off, you'll see). After you cut any length off the coil, the cups won't fit anymore. Therefore to avoid metal-to-metal contact, you can use two pieces of rubber gasket material to fit up into the upper hat for the coils to compress into. Make sense?