I'd like to know how someone would go about swapping out caps directly on the fly, and try to discern the difference. The Flash with clip-leads?
One way would be to rig up two different networks with different brand/type of caps, and somehow use a DPDT switch to swap between networks. Using just one side of an amplifier, or a mono amp.
You could quickly swap between networks, to hear differences. A friend and I did this once with a 2A3 SET, and some large Mitsubishi amplifier...DX some such...
We used one speaker with a switch to switch between amps. Once we had the volume levels set even between both amps, switching back and forth quickly showed no differences unless they were really subtle. One's (at least mine) audible memory isn't that quick to note subtle differences. YMMV.
But when you take 2A3 amplifier or the Mitsubishi, and listen to one of them in your system for a week, and then switch to the other, one will or should notice the differences.
I would guess that this the same for capacitor networks.