Glue Cover to Top
The cp-yoyo-cover.stl part will have a loose fit when placing it over the cp-yoyo-top-a.stl part, so you'll need to use some adhesives to perminanently bond them tgoether. I used super glue, but anything similar should be fine.
You can totally 3D print the cp-yoyo-cover.stl part. In order to get decent diffusion to allow the NeoPixel LED ligh to shine through, you'll need to use a light colored filament, such as natural white, transculent or glow-in-the-dark.