Required library edition:
Required library file: dhtmlxcombo.js

updates a specific option in the combo box

• oldvalue - (string) the current option value
• avalue - (string) a new option value
• atext - (string) a new option text
• accs - (string) a new style for the option

var z=new dhtmlXCombo("combo_zone3","alfa3",200);
z.addOption([
           {value: "a", text: "option A", img_src: "../images/red.gif", css:"color:red;"}, 
           {value: "b", text: "option B", img_src: "../images/green.gif"}, 
           {value: "c", text: "option C", img_src: "../images/blue.gif"}
]);
...
z.updateOption("b","b","New option B","color:green;");