https://sims4studio.com/thread/2310/cas-sort-layer
Changing the sort layer is done through the warehouse on each "CAS part". There is a CAS Part for each swatch and the sort layer will need to be changed for each one so, if at all possible, change the sort layer before adding a lot of swatches. Once you've changed the sort layer on the first swatch each swatch you add after that based on the first swatch will have the sort layer you gave the first. The Warehouse sorts sections within a resource in alphabetical order. Sort layer is down toward the bottom in the right hand panel: