Safe way to change cables with tube amp on...

Go ahead - try it! No guts, no glory...

But, before you do anything like that, make sure you have already ordered your new amp. 'Nuff said.

The resistor would theoretically avoid the no-load condition that might damage the amp. However, human error while you are messing around with the wires remains a hazard. Why risk it?

A agree this is not a wise thing to do for so many reasons. And putting a resistor across the amp? You plan on removing/reconnecting this resistor each and every time to swap cables on/off the amp? This only doubles the possibility of shorting the terminals on the back of the amp. The strip terminals on these older amps are a pain enough when the amp is off. And who said the amp necessarily needs a load when it is powered on anyway. Just because it is a tube amp does not mean it is unstable without a load. A call to ARC would answer this for your amp......but this whole process is only asking for trouble. And if a disaster occured, you would most likely become a recipient of a Darwin award. Don't do it.

'Nuff said, thanks for the advice. I've decided rather than using a resistor I just stick my tounge across the terminals heh heh. Seriously though I guess the old fashioned way of powering down is really the safest.
Cheers!