One could use Ernie's terminal block scheme or any other mechanical contraption that you can think of to make a wire size reduction. Really, you are simply adding a small additional series resistance that is not very significant compared the run of a couple hundred feet of wire. The limit, of course, is if the reduced section melts or causes a fire due to the current.

If you are majorly concerned about this, don't ever insert a fuse in speaker circuit.

I don't know about the present product line, the original Haffler power ampliers placed the speaker fuse inside the feedback loop in an an effort to minimize audible consequences. This would result in some unusual symptoms when the fuse blew because there was still a small amount of very distorted output -- making one believe that the amplifier was "blown". I would use this to my advantage in the store when dealing with a jerk. I had a 6th sense that one of these jerks would seize the Volume control and turn it up past "11". I kept the Haffler speaker fuse a little under size and used it for these demos. After a few seconds at "12" the fuse would blow, the amplifier would sound blown, and the jerk would leave. This was a lot quicker and easier than my throwing a fit and tossing them out. Further, it had the advantage that the jerk would tell his (they were always male) jerk friends about the wimpy equipment that I carried and they'd stay away too.