Due to the highly MMO-like nature of the game, players cannot alter anything about the match via console. There are, however, several chat commands and a couple of command-line switches available, although they're not entirely useful (and a large amount were disabled after beta).
A listing of available chat commands can be viewed in-game using the
I cannot find any sources that give a full listing of command-line arguments, but I can confirm two of them:
Using this switch will force the game into window mode.
This switch will bypass the updater and get you straight into the game, though I'm not sure how it will react if an update is available.
"Diablo III.exe" -w -launch will bypass the update and take the game directly to the login screen using window mode.
I will attempt to keep this answer updated as new information is revealed.