What to assign belly ring weights

Hmmm, Mauvemorn just explained something about this a couple of days ago here.

In a nutshell, you'd clone an accessory and you'd UV map your mesh into one of the accessory areas of the CAS map. What area you map your mesh to depends on what you cloned. For instance, if you cloned a bracelet your mesh would be UV mapped to the bracelet area of the CAS map. I shared the CAS map in that thread so download it and keep it. You will use it constantly if you continue to make CAS custom content. You'd open the image in the UV editor in Blender so you know where to place your UV islands.

When transferring weights, do what Mauvemorn instructs. Use the nude top that's in the rig and transfer weights from it since it has the belly weights as part of it. Then, use the addon to remove the weights your mesh does not need; when you transfer weights from a nude top, you'll end up with weights that affect the arms and so forth and you don't need those weights. The reason it's best to use the rig's nude top is that you won't have to clone a nude top, export the mesh, and then append it to Blender. It's just easier to use the rig's nude top.

Read through the thread I linked. Lots of info there.

Edit: Mauvemorn posted at the same time so some of the stuff I said is a repeat, lol. 

Also, I should note, most of my advice in that thread is wrong, but you can grab the CAS map there and, as Mauvemorn pointed out, you can clone an accessory to use for your final package but DON'T transfer the weights from the accessory. Transfer weights from the rig's nude top then remove unused weights.