Do Fuses make a difference ib sound?

If one has monoblock amplifiers, it would be easy to conduct an experiment. Just put an aftermarket fuse in one amp and leave the stock fuse in the other amp. You should hear a change in how the soundstage and imaging are presented from the side that has the aftermarket fuse. For me, it was subtle but audible. 

I would never put anything in a device other than a fuse of the recommended type. Aside from possible damage to the device, there’s also the risk of fire. I would really lose my s$!t if I burned the house down!

Unequivocally no.  They don't make a difference.  Sleaze bags like Synergistic Research counts on you believing his word salad and thinking you hear something that is NOT there.

I use the slugs also and my mono blocks are protected with a digital (electronic) breaker. I noticed a good change. The breaker on one was tripped and protected the amp as it should and resets itself. Highly recommended. 

@mggartner +1