You can do it in exactly the same way that you change the rowsource
for a combo box.

It's simplest if you use a Table as the rowsource; just add a record
to the table (or delete one) and requery the listbox.

I take it you are aware that a multiselect listbox needs VBA code to
do anything with the selections? The Listbox doesn't have a "value"
that can be stored in a table or used as a criterion; you need code to
extract the selected values.

                 John W. Vinson[MVP]