Do not change your user name until SMP updates to 1.8. If you change it, the server will not recognize you and you will loose access to your inventory, claims, TRANSFER VAULT. Staff will notify you when it is safe to change your name.
Currently there's a glitch with all player vaults, showing them as empty. Any items placed in the vaults right now will disappear. We are working on getting fixing it, but I recommend not touching your vault for the time being. This applies to everyone, not just people who changed their name. - Jupiter