here's the manual way:
import both the selestia model and milltina model
Drag and drop both models into the scene
Delete all meshes on the selestia except for the head
Go through selestia's armature except for the armature, hips, spine, chest, neck and head (and everything in the head bone)
Remove selestia's avatar descriptor
Delete Milltina's head and hair
Delete the Milltina head and the bones within the head bone (not the head bone itsself)
Drag the head-only selestia onto the headless milltina
scale and adjust the selestia head by her neck or head bone
Drag Selestia's head bone onto the Miltina head bone
Profit
