Linked Meshes cannot be moved to a different slot, as explained in the FAQ of Linked Mesh.
While I was working with my problem, I tried to create my layers within the same pixel dimension (height and width). However, since the dimensions cover as big as the entire body, the skeleton sheet would have a ton of space between each layers, increasing the file size of the sheet slightly, compared to using Spine's exclusive Layers to PNG script before generating the skeleton sheet.
However, a friend of mine suggested a nifty Photoshop technique that would alleviate my issue with Linked Layers' inherent problem for different-sized layers. I can possibly draw a universal "wide stencil" around, for example, an "arm" layer. It would be big enough to also cover a "glove" layer and I would apply the stencil on that layer as well. This would keep these layers' pixel dimensions the same, so when they are linked together, one of them will not multiply in size and get cut anywhere in an attempt to match the other. Then in Spine, the mesh can be edited to exclude / erase the "wide stencil".