\documentclass[
    a4paper,
    twoside,
    twocolumn
]{article}

\usepackage[
    hmarginratio=1:1,
    top=25mm,
    bottom=25mm,
    columnsep=20pt,
    footnotesep=1cm,
    left=25mm
]{geometry}

\input{x3-general-preamble}

% Add switch to disable the Abstract
\newif\ifDisableAbstract

\documentclass[
    a4paper,
    twoside,
    twocolumn,
    11pt
]{article}

\usepackage[
    hmarginratio=1:1,
    top=25mm,
    bottom=25mm,
    columnsep=20pt,
    footnotesep=1cm,
    left=25mm
]{geometry}

\input{x3-general-preamble}

% Add switch to disable the Abstract
\newif\ifDisableAbstract

Set x3-paper to 11pt fontsize
Set x3-paper to 11pt fontsize
