Changing the login name for user dbo
To the best of my knowledge you can't change the dbo user without changing the entry in sys.databases.  This is a case where the same piece of data (the owner of the database) is set it in two places.  While they do occasionally become out of sync they mean the same thing.

If you need someone to have database owner access then just add them to the db_owner role. Really the main difference between dbo and members of db_owner is that members of db_owner can be denied permissions while the actual dbo can't.