Aftermarket fuse to tame a bright system?

For now, do nothing.  You need to get accustomed to the new sound.  A lot of the break-in process, I suspect, is the listener breaking in, not the gear. Also, try not to move the new cables at all; let them rest in their current position so that static charges in the insulation stabilize and become evenly distributed. After that, you might need to tune the system if it still doesn't please you.  Any new addition is not something that you can drop in in place of something else; you have to make adjustments. 

The first adjustment would be speaker placement or listening chair placement because these are free changes.  Sometimes it is a shockingly small movement of the speaker will do it.  In particular, change the toe-in of the speaker to primarily alter the energy delivered by the tweeter.  Moving the speaker may allow you to find a placement with more bass reinforcement--more bass means the relative balance has shifted downward so the perceived brightness is reduced.  

I doubt that a quick and easy hardware solution, such as fuse swap will really do the trick if there has been a substantial change.  Perhaps the best hardware solution might be to put back one of the interconnects, or the speaker wire, s that the entire system is not cabled with the Audioquest stuff.

@gavin1977

I have two Synergistic Research cables (Kaleidoscope and Looking Glass) and an older XLO Ultra cable.  I do seem to lose some sq with those.  I also have a Morrow Audio MA-5.  No real complaints about it.  I have Core Power Technology Diamond cables.  They aren't bad.  

I think it's all about system matching.  I thought I had wasted my money on the Harmonic Technology cable.  It's been sitting in it's box for a while.  

The DH Labs Air Matrix is very good, too.  At least it is in my system.  

I haven't tried any super expensive interconnects.  My speaker cables were $1500, but I haven't spent nearly that much on ICs.  I like how my system sounds now, so I probably won't try more cables. 

IME an entire loom of silver cables is too much of a good thing. I like one copper IC in the mix somewhere along with some silver power cables and some copper ones.It's a process to figure out which goes where. I like silver on the front end and for speaker cables, then mix and match the others.

[to @gavin1977] As a quick test and self reminder of what just happened, try re-inserting a pure copper interconnect head of stream, back at the source, ahead of the downstream silver cables. You can move the cable up/down the stack and find a balance sometimes. As @jtcf noted it can be leaning you in a new direction with all silver cables in your system. Give it time or try testing a few ideas...

I do this some times with my current pure copper stack reinserting a silver-over-copper cable back in to the system to remember how silver can make things more tipped up depending where you locate it within your system. You can also try letting it sit for a while, letting it go as-is, see if it will mello out some in time, yet I always found my former all silver cable loom a bit more bright and tipped up than I liked fwiw.  A buddy of mine has my all-silver cable loom now in his very mellow tube system with a mello tube dac in the mix and it sounds quite nice.  Just a matter of finding a balance perhaps.