If you are still getting spelling errors in calibre, that means:
1) There are additional language declarations in the html files. You will have to change them as well
2) Install an en-AU dictionary in the calibre editor, it does not come with one by default. Or alternately, set the en-gb dictionary as the default for english.
As for changing the language in word, it is very easy, see
http://libroediting.com/2014/03/26/h...2013-document/