Mass Allow_br

I would like to add mass action into engine/inc/massactions.php for $allow_br, when we add or edit news there is option

    if( $row['allow_br'] != '1' or $config['allow_admin_wysiwyg'] == "yes" ) {
        $row['short_story'] = $parse->decodeBBCodes( $row['short_story'], true, $config['allow_admin_wysiwyg'] );
        $row['full_story'] = $parse->decodeBBCodes( $row['full_story'], true, $config['allow_admin_wysiwyg'] );
    } else {
        $row['short_story'] = $parse->decodeBBCodes( $row['short_story'], false );
        $row['full_story'] = $parse->decodeBBCodes( $row['full_story'], false );
    }
    
    if( $row['allow_br'] == '1' ) $fix_br_cheked = "checked";
    else $fix_br_cheked = "";
    
    if( $config['allow_admin_wysiwyg'] != "yes" ) $fix_br = "<input type=\"checkbox\" name=\"allow_br\" value=\"1\" {$fix_br_cheked}>&nbsp;{$lang['allow_br']}";
    else $fix_br = "";

I want this option to be added in mass action so I can edit multiple articles at once to add $allow_br, but I so so newbie, don't know how to start to add function, would you please be so kind help me add this mass action step by step...

Thank you very much.