Short answer no. The 821 will not like being told it is an 841; not even sure if it would load properly.
Are you trying to get more power out of your 821? Best bet is to play around with your voltage settings to see if you can squeeze a little more out of it.
it was a thought, i have 2-821's that I am going to start back up. I'll just mess with the settings like you said. Depending on how bored I get, i might see about compiling my own firmware.
Thanks.