You can use linked meshes as long as the images you would like to divert the mesh from are exactly the same size and in the same slot:
Mesh attachments - Spine User Guide: Linked meshes
If the images are different sizes or in different slots, they can be diverted to some extent by first duplicating the original mesh, then replacing its image path, and then editing the mesh vertices as needed.
Also, vertex positions can be pasted to a different attachment, as long as the same number of vertices is selected. The order the vertices were selected before copying and before pasting should match the order you want the positions to be applied.
Tools - Spine User Guide: Copy/paste
By the way, an idea of adding a feature that would make it easier to copy meshes is on our roadmap:
https://github.com/EsotericSoftware/spine-editor/issues/551
You can also check the thread linked to in the issue above for a log of discussions on this issue, if you are interested.
