One of the key features of the color separation script is the Custom White generator. A repeatable white is a big help when designing color separations, and once you get a setting that works for you they rarely need adjustment. The white generator uses both a Curve to adjust the values, and a Saturation Mask to control the overprinting of the Highlight White. In addition there is a set of custom color adjustments which can be used to reduce the white overprinting.
In this video I use the custom adjustments to reduce the amount of highlight printing into the Green and the Yellow. The same adjustments are also available in the Custom White script.