Currently, if you want to swap the user license type between two users, you need a third unallocated license to play musical chairs with, or to delete>recreate one of the users.
In a small organisation where they typically do not have spare licenses, we have come across situations where due to staff job description changes, they need to swap the user license type between two people. The only way to do that without a spare license, is to delete one user, allocate their old license to the other person and then recreate the user and add them to various groups etc. This seems very inefficient.
Esri should create a way to select two users and swap their user license type.
I am ware that in some cases, primarily where a Creator type is involved, it is a non-trivial task, but Esri should be able to work out how to transfer ownership of assets in the process. DM me if you want me to help the dev team work it out.