https://sims4studio.com/thread/3735/add-specular-resource-item

Introduction

This tutorial will show you how to add a specular resource to a CAS item that has no specular resource originally.

This tutorial assumes you have completed some of the basic Sims 4 Studio tutorials and have a general understanding of how to use the tool.

What you will need

Sims 4 Studio (Jackpot) - please note, this tutorial was not written to take advantage of new features added after the Jackpot version of Studio.

Instructions

For this tutorial I used the base game face paint as the example. Clone your item and click into the Warehouse. Select the RLE 2 Image line. Click the Add button:

When the Add Resource box pops up scroll to RLESImageResource and select it:

Click on the new RLES line that Studio adds and import your rles images. Remember to name them according to Studio's rles naming convention so that Studio pulls your new mask along with the overlay when you import:

Link your new specular in the CAS Part resource by copying the Type, Group, and Instance numbers from here:

into the corresponding lines here:

You need to do that for each CAS Part so it's best to do this part before adding swatches. If you link the first all subsequent swatches you add will be linked already.

Save your .package and continue working on the project.