for legendLyr in iface.mapCanvas().layers():
        if legendLyr.name() != "os1250_line" and legendLyr.name() != "os1250_text":
            renderer = legendLyr.rendererV2()
            if renderer.type() == "categorizedSymbol":
                myRenderer = renderer.clone()
                for cat in myRenderer.categories():
                    cat.setLabel("foo")
                    print(cat.label())
                legendLyr.setRendererV2(myRenderer)
                for cat in legendLyr.rendererV2().categories():
                    print (cat.label())
                legendLyr.triggerRepaint()