It is done all the time. Bias rarely needs much change,, but you do need to adjust the output impedance. In other words your 16 ohm cab now plugs into the 8 ohm output.
You have to be aware some amps will not work like that. Peavey Valve King amps for example run the power tube heaters in series, so pull any and they ALL go dark. Same with Classic 30.
But you said the magic word: loud.
Power and loudness are not the same thing. Cut power in half and it is only 3db less loud. NOT half as loud, just 3db.