I'm not sure that guide answers your question, though.
I think the right course of action would be to name your new repository packer-plugin-amazon-ami-management
Then, when you register the post-processor in the new server, make sure to register it using the plugin.DEFAULT_NAME variable. That will tell Packer to use the plugin root name (amazon-ami-management) as the reference name for the post-processor.
Then, open a docs PR so we can link to you from our "community post-processors" page, or open an issue with a link to your new repo so I can do it for you :D