overtake What you're looking for is something like the Live2D feature, right? Spine's meshes are very different, so I don't think we'll ever add the ability to nest meshes. Instead, we have had an idea for a long time to allow meshes in different slots to become linked meshes for a while: EsotericSoftware/spine-editor195

We recognize that this should be a high priority and hope to implement it in v4.3 or a near future release.

overtake If Inherit Deform is unchecked in the properties of the linked mesh, the linked mesh can be deformed independently without affecting the source mesh. However, the only deformation that can be done here is by adding deform keys, and you should note that deform keys can have a negative impact on performance at runtime.

Spine basically uses bones to perform transformations, and weights can be used to adjust how much each mesh is affected by the deformation of its bones. It is possible to set the weights so that all hair strands are affected by the same bone, or to set a bone to affect all bones attached to each hair strand, making it easy to control large numbers of hair.

We may be able to give you more specific advice if you show us the rig you are actually having trouble with.