Is your weapon animated as well?
If not, the easiest way is to merge the role and weapon(s) into a single Spine project, then use skins and skin placeholders to be able to switch between multiple slots.
If you need to combine two animated skeletons (one for the "role", one for the "weapon"), there's currently no easy way to do this at runtime. You'd have to modify SkeletonRenderer so it can render another skeleton in between two attachments being rendered for the first skeleton.
