I am not sure what you mean by "fire an event"
You can certainly have a custom button call VBA code (that normally how I
use custom menu items).
That code can most certainly "call" some event code you have in a form.
So, if you wanted to call the after update event of a particular control,
say "company" name after update event, the you could simply put a pubic
function in your form call
Public Function MyCoAfterCall
Call CompanyName_AfterUpdate
end if
and, then for the custom menu/tool bar on-action, you go
=MyCoAfterCall()