No, they don't adjust the packing on the muffler. They add resonators to the pipe to quiet it down.
Loud has just the muffler, medium the muffler + resonator, and quiet muffler + 2 resonators..
I had the quiet on, but I got rid of it as it still droned quite a bit on the highway during long drives... Nice deep growl to it, similar to the stromung (although those I know with the stromung had rust after 1 winter, the brullen was fine after a year).
The fit wasn't that great, I had to have brullen drop the muffler a couple of inches as it was burning my bumper.
I wound up with an Apex'i N1 exhaust, and although it looks a lot more conspicuous than the brullen (5" melon launcher vs. dual 3" tips) it's MUCH MUCH quieter, has a nicer tone and flows a lot better (butt dyno)