Update layer symbology with arcpy

update_symbology.py

import json

import arcpy


def resize_symbol(layer):
    if not layer.isFeatureLayer:
        return

    symbology = json.loads(layer._arc_object.getsymbology())
    if symbology['renderer']['type'] == 'simple':
        if symbology['renderer']['symbol']['style'] == 'esriSMSCircle':
            symbology['renderer']['symbol']['size'] *= 3
        if symbology['renderer']['symbol']['style'] == 'esriSLSSolid':
            symbology['renderer']['symbol']['width'] *= 3
    else:
        for break_symbols in symbology["renderer"]["uniqueValueInfos"]:
            if break_symbols['symbol']['style'] == 'esriSMSCircle':
                break_symbols['symbol']['size'] *= 3
            if break_symbols['symbol']['style'] == 'esriSLSSolid':
                break_symbols['symbol']['width'] *= 3

    layer.updateLayerFromJSON(json.dumps({'drawingInfo': symbology}))


layers = arcpy.mapping.ListLayers(arcpy.mapping.MapDocument('CURRENT'))
for layer in layers:
    resize_symbol(layer)

arcpy.RefreshActiveView()