When the parameters of a geoprocessing service change, the only way I can get the geoprocessing widget to show the new parameters is to remove the widget altogether and re-add it, including all the other widget configuration that's needed. Would be nice if there was a refresh button or if the widget responded to the "Set" url by repopulating the parameters.
Ted,
This sounds like a great enhancement request. The way you get enhancement requests logged is by calling esri tech support and walking a technician though your workflow and asking for the desired behavior to be logged as an enhancement.
This might even be worth posting here Esri Arcgis Ideas | Ideas Submission Portal