Good morning Jonathan,
Please have a look at the example below. This script allows you to get your item and to update metadata items like the snippet, the description, the Terms of Use, the credits and one or more tags.
HTH,
Egge-Jan
from arcgis.gis import GIS
my_agol = GIS("https://www.arcgis.com", username, password)
my_item = my_agol.content.get('<itemID>')
service_snippet = 'Here you can put a short snippet describing the Feature Layer'
service_description = 'Here you can put a description of the Feature Layer'
service_terms_of_use = 'FOR INTERNAL USE ONLY'
service_credits = '© Me, myself and I'
service_tags = ['Railway','Canada']
item_properties = {'snippet' : service_snippet,
'description' : service_description,
'licenseInfo' : service_terms_of_use,
'accessInformation' : service_credits,
'tags' : service_tags}
my_item.update(item_properties)
Modified Metadata
Via Child Resources > Info > Metadata you will get to an XML with your modified values (see screen dumps below).