...
        newDatasource = urllib.quote_plus(wfsURI)
        WFSLayer.setDataSource(newDatasource, wfs_layer_name, "wfs", True)
        WFSLayer.reload()

segmentation error

# first instance of WFSlayer
url1 = "http://myServer.com/geoserver/wfs?version=1.0.0&service=wfs&typeName=StoreName:layerName1&request=GetFeature"
WFSlayer = QgsVectorLayer(url1, "layer1", "WFS")
QgsMapLayerRegistry.instance().addMapLayer(WFSlayer)
QgsMapLayerRegistry.instance().removeMapLayers( [WFSlayer.id()] )

# second instance of WFSlayer
url2 = "http://myServer.com/geoserver/wfs?version=1.0.0&service=wfs&typeName=StoreName:layerName2&request=GetFeature"
WFSlayer = QgsVectorLayer(url2, "layer2", "WFS")
QgsMapLayerRegistry.instance().addMapLayer(WFSlayer)

# delete existing features
idF = []
for f in WFSLayer.getFeatures():
    idF.append(f.id())
WFSLayer.startEditing()
for idFea in idF:
    WFSLayer.deleteFeature(idFea)
WFSLayer.commitChanges()

# new temporary layer
v_layerNew = QgsVectorLayer(uri, wfs_layer_name, "WFS")

# add new features to old layer
WFSLayer.startEditing()
for feature in v_layerNew.getFeatures():
    WFSLayer.addFeature(feature)
WFSLayer.commitChanges()