F9 is the short cut to requery combo and listboxes on forms, but it means you have to tell your users to use it, and they have to remeber to use it.
This is an alternative that you can use on all of your forms when you modify the data in a combo box. Rather than using a requery even for each combo box, it will find any combo boxes in the main forms of you application that are open. I don't have a sub form requery code written but i'm sure i'll get around to it soon enough:
Place this in a module and call it whenever you modify the contents of combo or list boxes.
Public Sub RefreshComboBoxes()
On Error GoTo eh:
Dim frm As Form Dim obj As Object Dim oCtl As Control Dim sbfrm As Form Dim oCtlSub As Control
For Each obj In CurrentProject.AllForms If CurrentProject.AllForms(obj.Name).IsLoaded Then Set frm = Forms(obj.Name) For Each oCtl In frm Select Case oCtl.ControlType Case acComboBox, acListBox oCtl.Requery End Select Next End If Next obj