How to add custom Meta-Data?

I have been researching Cesium’s meta-data system, and would like to be able to add my own to the Cesium tile set.

I mainly want to mask and sample different terrain types (which I would specify manually in the meta-data). I assume I would want to use Feature ID Texture Metadata specifically, but knowing how to add all types of meta-data would be very helpful in the long run.

Is this feasible? Is there any documentation on the subject that you could point me to? Thanks in advance.