GiD_Event_BeforeInitGIDPostProcess: will be called just before changing from pre to postprocess, and before read any postprocess file (this event can be used for example to check the results file existence and/or rename files). It has no arguments.
If it returns -cancel- as a value then the swapping to postprocess mode will be cancelled.

proc GiD_Event_BeforeInitGIDPostProcess {} {
}

GiD_Event_InitGIDPostProcess: will be called when postprocessing starts. It has no arguments.

proc GiD_Event_InitGIDPostProcess {} {
    ...body...
    set value ...
    return $value
}

GiD_Event_AfterSetPostModelName

proc GiD_Event_AfterSetPostModelName { name } {
}

GiD_Event_EndGIDPostProcess: will be called when you leave Postprocess and open Preprocess. It has no arguments.

proc GiD_Event_EndGIDPostProcess {} {
}