I recommend that you use REQUERY
the specific combo box whose data you have changed AND that you do it after the Cmd.Close
statement. that way, if you were inputing data, that data is also requeried.
DoCmd.Close
Forms![Form_Name]![Combo_Box_Name].Requery
you might also want to point to the recently changed value
Dim id As Integer
id = Me.[Index_Field]
DoCmd.Close
Forms![Form_Name]![Combo_Box_Name].Requery
Forms![Form_Name]![Combo_Box_Name] = id
this example supposes that you opened a form to input data into a secondary table.
let us say you save School_Index and School_Name in a School table and refer to it in a Student table (which contains only the School_Index field). while you are editing a student, you need to associate him with a school that is not in your School table, etc etc