hi
you can use this JS code:
var low = {value : 100000000, text : "Low"};
var medium = {value : 100000001, text : "Medium"};
var high = {value : 100000002, text : "High"};
var pickList = Xrm.Page.getControl("control_name");
var options = pickList.getOptions();
for (var i = 0; i < options.length; i++)
pickList.removeOption(options[i].value);
pickList.addOption(low);
pickList.addOption(medium);
pickList.addOption(high);
