Lighter springs require lighter(less) rebound damping as you say. The forks will pack because the lighter springs will not have enough force to push past the heavier valving for the heavier springs. Packing will cause harshness, headshake, and will disturb handling characteristics.
You can run a rate down from factory without changing anything but you'll have to run the rebound clicker way out (like 17-18 clicks) which increases midvalve bleed and can have some negative side effects such as pushing in corners while still having it pack on large successive hits.
The stack before the stock crossover is alright but the high-speed portion of the stack needs lightened with lighter springs.
Ahhh. Thanks for the explanation. I wasn't seeing the bigger picture.... the clickers are only part of what controls rebound. Also, if it's appropriate in this forum, is there a place(s) you recommend that will do the right rebound adjustment for lighter springs? Also, if I went down one spring rate on the shock, would a similar rebound readjustment need to be done? Thanks.