Adding or removing shok buff's does not change the available space for the recoil spring to compress. No need to cut a recoil spring if shok buff's are used.
Cutting coils does not change the over all rating of any spring. For example, a 16 lb spring remains a 16 lb spring after cutting coils.
Cutting coils does increase the spring rate per inch. The overall rate such as 16 lbs is different than the spring rate per inch.
The overall rate of a compression spring is a function of each individual coil. For example a 16lb spring can be a few coils, as each coil needs 16lb to fully compress that coil.
Since a spring that has had coils cut is now shorter, there is less dimension for the spring to go from zero to 16lbs. Thus the rate per inch increases.