Yes, you can duplicate and flip meshes in Spine to create mirrored versions of parts like arms. Here's a general approach based on the information provided:

1. Duplicate the Mesh: First, create a duplicate of the mesh you want to mirror. This can be done by selecting the mesh and using the duplicate option.
2. Mirror the Duplicate: To mirror the duplicated mesh, you can set its scale to -1 on the axis you want to mirror it across. This effectively flips the mesh. Make sure the duplicated mesh is aligned correctly with the original to ensure symmetry.
3. Adjusting Vertices: If necessary, you can adjust the vertices of the mirrored mesh to fine-tune its position or shape. This might be needed to ensure that the mirrored mesh perfectly matches its intended position as a left or right counterpart.

It's important to note that while this method allows you to create a mirrored version of a mesh, any specific rigging or weights applied to the original mesh will need to be adjusted or reapplied to the mirrored version to ensure it behaves correctly during animation.

For more complex rigs or when mirroring specific elements, you might need to consider additional steps, such as mirroring bone hierarchies or adjusting inheritance properties for certain bones, especially if they have unique behaviors or constraints.

Everything above is correct! If you're more of a visual learner, here is also an example video where mirroring of meshes and parts of the skeleton happens: