Previews
The preview is generated at the end of the create process using the preview scene included with Catalyst.
Show/Hide Inputs
If you want to hide an input in the menu, click on 
Customize thumbnail
You can customize the preview scene by going into the addon folder and edit the preview_scene.blend.
Customize Preview Scene
If you customize the preview scene, do not change the camera or ground position as it is used to place the asset at the correct position during the render. You can customize the materials and the lights as you like.