Normally I'd guess that you have weird transforms or frozen transforms on your blend shape source. You could try using match transforms in that case. But it looks more like it's sliding along one of the head bones, were transforms frozen before you skinned it? Head mesh as a child of a head bone?
Which bit are you struggling with ? copying a transform is simply a case of assigning a node's transform to a variable (t = node.transform) applying a stored transform is simply a matter of assigning a variable to a node's transform (node.transform = t) if you work in a rollout, anything you store will persist as long as…