To achieve the desired hierarchy where the R_arm layer is nested under a R_arm bone within the torso bone, you can use the [bone] tag to create a bone for R_arm and then manually adjust the hierarchy in Spine after import. Unfortunately, the current tagging system does not support directly specifying nested bone hierarchies through tags alone. You can tag R_arm with [bone] to ensure it creates a bone, and then after importing into Spine, you can manually move the R_arm bone under the torso bone in the hierarchy.

Here's how you can tag your layers:

R_arm [merge] [bone]
torso [bone]

There is no need to specify the bones in the PSD if you have an already established Spine file you are importing the images into. As long as the slot names match, Spine will automatically populate the slots with matching names, even if they are already parented to other bones.

mrobot

Since Photoshop and similar softwares do not complain about folders having the same name, if it is not a problem for you, you can just have two torso [bone] folders like in the image below.

Does this solution fit your needs? Otherwise, as Erika said, you can just import once without a bone structure, then let Spine place the slots in the right place.