I didn't have any issues with the carbon fiber on the Bking, and the Busa mufflers were aluminum with a fake cf wrap.
I have seen quite a few cf mufflers fade/discolor over the years, and age and the sun are obviously to blame. They were all different brands.
I have had several cf mufflers on different bikes over the years, and never had any problems. Then again, every bike was always covered or garaged when it wasn't being ridden. They were all Yoshimura and Akrapovic too though. The only reason I had the 2bros is because they were on the Bking when I got it.
The great thing about the cf is that you can run the bike hard all day, and still lay your hand on the muffler.
That being said, I would think that a clear coat wouldn't burn off. But I'm no painter, and wouldn't want to give advice on that.
Some discoloration over time is going to be hard to avoid.
As far as the packing goes, I'de leave it alone. The packing itself burns up over time, and eventually the exhaust will become slightly louder. But that usually takes a long time. If the packing has deteriorated enough, it will transfer a little more heat through the shell of the muffler, as opposed to out of the tail pipe. That may/may not help to discolor the cf over time.
The packing in a new or relatively new muffler is fine. It's your choice if you want to try and add a little more. But if you do, I don't know if it would be beneficial. You can look at the packing and tell when it's had it. It'll be noticeably black and charred.
Now I have little experience with 2bros, so your friend's advice may be sound. Maybe the amount of packing in the 2bros is slightly less than other brands, but I could not say. The mufflers will be apart, so if you want to change or add packing, go ahead for your own piece of mind. I have noticed a difference in the finish of 2bros compared to other brands, nothing bad, just different. And I have seen them look dull in much shorter amount of time than other brands. So maybe their finish process isn't as good as others, but I cannot say.
I personally am not a fan of 2bros anyway. I find them obnoxiously loud, unless you pay $80/$90 for baffles/tips that other companies include for free. I don't like the looks of most of them either, but these are just my own opinions.
For the length, unbolt the muffler from the midpipe and have someone hold it for you. Have them move it down until it looks good, just eyeball it, then measure.
I'de start with no more that 3" to 4". Then just push the end cap back on and put the muffler(s) in place.
Once you like the look you can go back and drill the new rivot holes and attach the end cap, or cut off more first. I'de put a layer of masking tape on the area you're going to cut too. Put your cut mark in the middle. The tape can help the cf from splintering as you cut it. I've always cut aluminum and cf mufflers with a fine tooth blade on a bandsaw. Of course that's not the only way, but it works very well and makes it easy to get a straight cut.
I don't remember exactly how much I cut off the Busa, but I think it was 6".
I personally don't like the look of the logos on the mufflers(just me), so if you noticed on the Bking I switched the end caps so the logos face in. You can even drill the logo plate rivots and remove them, which is what I did on the Busa. With the logo side to the inside you'll never notice the 2 rivot holes. You also cannot hear any exhaust leaks from them.
Once you shorten the mufflers you'll notice more of a change in tone than them getting louder, unless you cut them in half or a lot of them off.
