<p>I would like to change the "Row Source" values in an Access table through code.
This way I can filter what a user can choose in a column's combo box.</p>

I don't know whether or not this is an option for you, but I would recommend separating the table and filtering options, setting up a form to do the data entry and modification and using code to set the Row Source for the combo box on the form. As you've already seen, while Access does provide the opportunity to treat tables as more than just tables, that is primarily for GUI purposes. Behind the scenes, Access prefers that you work with forms for data entry.
If you need to pursue the table method, you might try looking at the MS knowledge base articles referenced
here
. (The kb articles are
here
and
here
.) Keep in mind that these refer to Access 97 and may no longer be relevant. I wasn't able to find any more recent references to those properties in an Access tabledef.