If you have the Anniversary Edition, there is no resistor change needed. Just crank up the bias trim pot (on the back) until you get 100 mA on the meter. On my 211's, I had to crack the trim pot all the way up before any bias current was evident.
I would recommend first turning the bias all the way down, then power off and swap the tubes, then power on and rebias.
I would recommend first turning the bias all the way down, then power off and swap the tubes, then power on and rebias.