documentclass[left=0cm,right=0cm,top=0cm,bottom=0cm]{article}

usepackage{geometry}
usepackage{lipsum}

begin{document}
    lipsum[1-10]

end{document}

documentclass[landscape]{article}
usepackage{lipsum}
begin{document}
lipsum[1-10]
end{lipsum}

DeclareOption{landscape}
   {setlength@tempdima   {paperheight}%
    setlengthpaperheight {paperwidth}%
    setlengthpaperwidth  {@tempdima}}

documentclass[landscape]{article}
usepackage{geometry,lipsum}
begin{document}
lipsum[1-10]
end{lipsum}

documentclass{article}
usepackage[margin=0pt]{geometry}
%...

documentclass{article}
usepackage{geometry}
geometry{margin=0pt}
%...

documentclass{article}
PassOptionsToPackage{margin=0pt}{geometry}
usepackage{geometry}
%...