Hi,
Have you tried adding the happy head as a morph target of the neutral head? That would probably be the best way. Either way, to swap heads simply make the old head invisible and set the new head as the face:
Code:
neutral = viz.add('neutral.vzf')
happy = viz.add('happy.vzf')
avatar.face(neutral)
#Swap faces
neutral.visible(0)
avatar.face(happy)