What would happen if?

I also would advise against it, for the reasons stated by Detlof and Xti16.

I wouldn't do it but also for comparison reasons. Wouldn't the unconnected pair impart unneccessary capacitance at the amp's outputs? Good luck.

when you do it, just be very sure not to let the disconnected ends touch...

alternatively while not as satisfactory but spark free - you might start by wiring one speaker with the old and one with the new to get an initial sense of significant differences.

you will need to run this for a few days to let the new cable settle in - rapid ABing can be very deceptive and is generally not considered to be a good way to tell much of anything - also it will give your ears time to listen and determine what differences you might in fact be hearing

if you decide there are some big differences then you could proceed to a more ambitious comparison

if there is not much difference you can decide which cables you are keeping and which you will be posting on the Gon

Oh go do it. I don't think that the second set of cables left attached to the amp changes any of the parameters of the amp at all. Think about it......

But, shorting is a REAL issue! What I have done when necessary is to tape the wires with spades so that the + and - wires are well away from each other and can't under any circumstances touch. Ditto for banana plugs if they are individual plugs (not two encased in plastic, seperated the proper space to match to many speaker and amp connectors).

Re the taping, hell I'm so anal about the shorting potential I tape all of my loose ends, spades, bananas, whatever, so they can't short if one or both were to come loose from the speakers or amps. Highly recommended!

FWIW.

I'm with Newbie on this one... just do it. it's temp anyhow.

You must have a completed circuit for electrons to move - conduct.

Connect and disconnect whatever, with the amp dead off. Once amp connections are made put whatever cables onto whatever speakers. Only one leg (one positive or one negative) of the cables not being listened to needs be disconnected to prevent any current flow into those 'off for now' speakers.... not both. Of course, insulating the exposed leg so it won't touch it's proposed binding post is important.

A balloon or tape, or a shoe or phone book... anything preventing conductivity will suffice.

Just 'member, power off the amp prior to making up and unmaking ANY connections to the speakers themselves.

As was said above about A/B ing, I'd shy away from instantaneously attemnpting that event. Given the power up and down safety measures you'll want to take, it's not viable anyhow. Just take notes instead.