We can now change Minecraft usernames through your account page on Mojang’s site!
Your inventory, the place you logged off, and most other things will stay the same.
[size=150]However:[/size] Be aware, you won’t be able to access chests or doors you protected prior to name changing.
Before changing your name, add your soon-to-be new username[color=#F00]*[/color] to the protected blocks, or temporary remove protection from them (hint: use /cremoveall). Then change your name, come back on, and reclaim all the chests you need to protect again (hint: use /cpersist to persist the command)!
Best of luck!
[size=85][color=#F00]* You won’t be able to break your own chest if you take this route.[/color][/size]