Hide Global Option Set values Conditionally

Hi,

I want to hide/show Global optionset values based on condition but i am not able to do that.

i am using below code.

if (Xrm.Page.getControl("field") != null)

{

            var PickListControl = Xrm.Page.getControl("new_OPtionsetField");
                PickListControl.removeOption(798210001);
}

I have called it on OnLoad trigger but it is not working. Please suggest

Regards,

Anand