My first Naim amp was a 5i, to use with a pair of PMC 23s. The dealer had advised me that as I was using my old biwire spkr cables I should join each pair at each end to use 2 cables into each plug, rather than have spare unused. After carefully making off the ends and checking there were no crossovers I plugged it all in and switched on. Nothing, except a brief flash of the input selector lights. Repeat, same, and no sound. Then I triple checked the spkr cables and found that I had indeed joined +ve to -ve on one channel. I corrected it and it worked brilliantly till it went in as a p/x for a 250.
I suspect that Naim build in protection against such idiocy, but choose not to announce it.
Anyway. In answer to the original question I don’t bother switching things off and on again just to change cables, speaker or otherwise. Volume to zero and care with any loose ends is ok. It occasionally feels that people are too cautious, when the risk is almost zero.