Is it possible to spoof names in a channel?
Nope.
If you can hack the Battle.net Protocol... maybe it is posible after all! In other words... No
How was/is it done for games? Do you just send something differently?
SC games are peer to peer. You can say you are whatever you want to be and everyone else will believe it.
Channels are server-sided. The server tells you who you are, and you listen to it.
Oh. Alrighty then.