Note attachments can be the same size but in a different position.
Spine doesn't have a way to remove the magenta. Ideally the background is transparent rather than magenta. To get that you'd need to export without Trim whitespace checked, or create the images without running the script.
It's a good approach and mentioned here:
Runtime Skins - Spine Runtimes Guide: Creating attachments
Using that approach, you don't need to rig your additional images in Spine. You can rig just one attachment of each type, like a template, so you know where it is positioned. Then you can create many images of the same size for that position. You can pack them in your atlas (or pack an atlas at runtime dynamically), then at runtime you create an attachment that references the atlas region. You'd place the new attachment in the same position as the "template" attachment.
A similar way to do it is the same but then modify the template attachment, changing its atlas region, rather than creating a new attachment. That can work when you only have one skeleton instance.
This approach allows you to have hundreds or thousands or more images without rigging them in Spine, which can be a huge time savings.
