DeclareOption{test}{%
    fancypagestyle{aSix}{%
    }
}
ProcessOptions
newenvironment{test2}{%
fancypagestyle{aSix2}{
%Takes the pagestyle aSix and update it with additional values}

ProvidesClass{ishouldgivemoreinformation}

newififaSix
DeclareOption{aSix}{globalaSixtrue}


ProcessOptions

LoadClass{article}

RequirePackage{fancyhdr}

fancypagestyle{aSix}{%
  fancyhead[C]{Foo}
  renewcommand{headrulewidth}{5pt}
}

ifaSix
fancypagestyle{aSix2}{%
  pagestyle{aSix}%
  fancyfoot[c]{Foobar}%
  % Some updates here
}
else
fancypagestyle{aSix2}{%
  pagestyle{aSix}%
}
fi

endinput

documentclass[aSix]{ishouldgivemoreinformation}


pagestyle{aSix2}
begin{document}
FOO
end{document}