Blockland went steam only earlier this year due to an RCE exploit. Update your blockland, and associate any keys you want to associate with steam at this link:
http://blockland.us/steam-redeemKey.phpYou can swap between alts with an ingame gui now if you have multiple keys associated with a single steam account. Name changing has been removed - new or unnamed accounts (default Blockhead####) get to set their name once iirc?
To play blockland you need to have steam open in the background so that the steam auth can authenticate your copy of the game.
If you have any revoked keys do not associate them with your steam account as that will nuke all other associated keys.