https://sims4studio.com/thread/442/make-sims-pose-using-studio

Introduction

This tutorial will show you how to create a custom Sims 4 CAS pose .package. It will not show you how to use Blender to make the pose itself. Because of limitations on how these pose .packages can be used in CAS I make my poses rotate so the person using it can easily view it from all angles. This tutorial will show you how to do that.

This tutorial assumes you know how to make a pose using Blender. I've written a tutorial showing how to use Blender to make a pose and posted it HERE. Please use the beginners pose tutorial in addition to this tutorial if you are unfamiliar with Blender or with Sims posing. This will save you a lot of time and frustration.

Until there is a Pose Player type mod for CAS all custom poses must be put in the game as default overrides of CAS trait animations. Once there is a means of playing custom poses in the game Studio is ready to enable custom poses and animations.

What you will need:

Sims 4 Studio

Instructions:

2. Type the word trait into the search bar. Select a a_CAS_trait to overwrite.

5. Click Create New. This will give you a blank Clip with the same number of frames as whatever Clip you selected. You can click the dropdown to select the model you want to work with.

6. Once you have named the .blend it will show up in Blender. If you selected Create New the model will show up in the bind pose. Create your pose at frame 0.

9. Slide the time bar to 80 or just type 80 into the current frame box. Deselect all the joints by clicking a on your keyboard again. Select the b__ROOT_bind__ joint, click 7 on your number

11. Slide the time bar forward to 85 or type 85 into the current frame box.