Accessing CAS modifiers from script

I've tried putting the example code into a python script for the game, but it doesn't work. @SimGuruEugi, any idea why? Sorry if this is incredibly obvious, as I am terrible at python, so any help would be appreciated!

import server_commands.argument_helpers
import services
import sims4.commands
from protocolbuffers import PersistenceBlobs_pb2


@sims4.commands.Command('cas.randomize_facial_attributes')
def randomize_facial_attributes(opt_sim:OptionalSimInfoParam=None, _connection=None):
    
    sim_info = get_optional_target(opt_sim, target_type=OptionalSimInfoParam, _connection=_connection) 
    if sim_info is None:
        return False
    
    facial_attributes = PersistenceBlobs_pb2.BlobSimFacialCustomizationData()
    facial_attributes.MergeFromString(sim_info.facial_attributes)
    
    for modifier in itertools.chain(facial_attributes.face_modifiers, facial_attributes.body_modifiers):
        modifier.amount = random.random()
        
    sim_info.facial_attributes = facial_attributes.SerializeToString()
    return True