I know that it is possible to update the item_properties for an item as outlined here Managing your content | ArcGIS for Developers .
I am writing a script to automate the migration of some Portal applications from dev > test > prod. Our team has maintained the same item 'id' for the application in the past by using ArcGIS Online Assistant (you can edit the json and change the id). That way our users can maintain a bookmark to the application in their browser (the id is part of the url).
Is it possible to edit the 'itemid' or 'id' using the Python API? If not, is there another way to programmatically update it?
Yes, programmatically at 10.8.1+, at least for ArcGIS Server Map/Feature services: