DBasic

$("#some_id")
    .autocomplete({
    ...
    }).data("ui-autocomplete")._renderItem = function (ul, item) { ... };
    
If you want to create the _renderItem function for multiple autocompletes with id #some_id just use it in the create event:
    
$('#some_id').autocomplete({
    create: function() {
        $(this).data('ui-autocomplete')._renderItem = function (ul, item) { ... };