I want to create a new head for the Poser male (Hi-Res Old Man) and I don't want to use morphs, I am planning to use Rhino. I know one can replace the existing head with a prop. However I want to import a new head with custom morphs and "stick" it permenantly to the poser male. How should I go about this? Is it possible or do I have to create a completely new figure in a modelling program and go through the whole joint Hierachy/ PHI thing?

You can just replace the head, then make the morphs within Poser using the magnets, but the mouth/jaw morphs should ideally be done in a modeller, then imported as morph targets.