jQuery Grid Plugin - jqGrid

My grid has a custom search area contining a single select control always appearing above the grid; when the search changes, of course, the data is refreshed. but the grid definition is not.

My grid definition contains another select box. The contents of this box depend on what was selected in the search option select.

When I change the search criterion, I want to change the option list for this second select box.

I think this can be done using the .aftersearch Function() event and an ajax call to get the list of options (as described in the examples).

The example shows how to update the select options on the edit form (once, when it is initiated) so it refers to (for example)

I don't want to call this every time the edit form is displayed, but once is not enough because the search criterion on the grid may have changed.

My question: can I update the returned values to the column in the colModel (and if so, how) or do I have to redefine the grid on every search?

Thanks,

Reg