I have done some experimentation with that, Elemenopee, but like I said before I'd prefer to find an alternative method (if there is one) because I don't want to have to redo my tweaks.

If you do the conversions properly (ie. so the poly mesh is identical to the poly proxy) the resulting sub-d mesh after the process theoretically should turn out exactly the way it was before (but merged of course).... but when I tried this it lost most of the creases i had made and then randomly and assymmetrically added creases in other places!

Unfortunately my 3 questions still remain.