You can! You just get an attachment and set it on a slot. The method Skeleton SetAttachment can do this for you using slot and attachment names, eg: Eg:
skeleton.SetAttachment("slotName", "attachmentName");
// Using names from your screenshot:
skeleton.SetAttachment("Weapon", "Sword");
Alternatively you can use Skeleton FindSlot to find the slot, Skeleton GetAttachment or SkeletonData FindSkin and Skin GetAttachment to find the attachment, then set the Slot Attachment.
You can read more about it here:
Runtime Skeletons - Spine Runtimes Guide: Changing attachments
