Hello Ichiro. My english is really bad. But if i understand your problem, i can help you.
if you use external menu(external exe files)and file_open_read for antialias variable, players can set the level of antialiasing.

you need ifdef for main.wdl;

Html:
ifndef aa_9;	
ifelse; //aa_9 ise
	var d3d_antialias=9;
	function main()
	{
		
		
	}
endif;

ifndef aa_4;	
ifelse; //aa_4 ise
	var d3d_antialias=4;
	function main()
	{
		
		
	}
endif;

ifndef aa_1;	
ifelse; //aa_1 ise
	var d3d_antialias=1;
	function main()
	{
		
		
	}
endif;
ifndef aa_0;	
ifelse; //aa_1 ise
	var d3d_antialias=0;
	function main()
	{
		
		
	}
endif;


end external settings file codes;
Html:
function start_func()
{

	if(antialias_var==0)
	{
		exec("..\\game.exe"," -d aa_0");
	}
	if(antialias_var==1)
	{
		exec("..\\game.exe","-d aa_1");
	}
	if(antialias_var==4)
	{
		exec("..\\game.exe"," -d aa_4");
	}
	if(antialias_var==9)
	{
		exec("..\\game.exe"," -d aa_9");
	}
	exit;
}


Like this;