If you believe that cable affects the sound then longer cable should affect it more, but your cable can be so transparent that 50% difference won't be audible. I still would not do it for the reason of resale value that Wolf_garcia mentioned.
Mono amps and different length speaker cables
Wondering if there is any noticeable negative effect from using say a 3 meter pair of speaker cables to one set of binding posts on the amp and speaker and using a 2 meter pair of the same brand and model of cable to different binding posts on the amp and speaker. I am using solid state mono amps.