> how about using a postamble function instead of html-postamble-format

Does it mean that I need to look into modifying the org-html--build-pre/postamble function?

If so, I will start looking into it but it will take a while as it full of elisp that I have never used (until today maybe): format-spec, plist-get and a lot of assoc's and assq's :)

Kaushal