Wordpress does not allow users to change usernames. As a service to help clients improve security, we go through the process of setting up more secure Administrator credentials and delete the very common user name of "Admin."
I noticed a client had a custom build plugin whose functionality depended on not only on just having Administrator role, but the ID of 1. Doing what we do, the new administrator does not have an ID of 1. This was easy enough to fix for this particular client, but is this a gotcha I need to look out for in Core? Does core have any functionality that relies on User ID 1? Are there any other implications of not having a user ID 1 in the database?