Uh, yeah. I don't have a copy of BL @ work right now, so I can't give you command offhand but its something like $Pref::Server::Name = "blahblah"; <-- NOT sure if that's exactly right.
If you go into Blockland\config\server\pref.cs aka find your preferences file you can get the command directly from there.
Also, atleast on MY computer, if you change the name and hit F2 to bring up the player list, the name will be the same. If you check the server list, or rejoin the game it should be changed though.