Installed "quieter" cores in my recently installed Mark's 4-2 exhaust. I loved the original sound, but I thought they were going to be too loud for my wife, when she rides on the back. The new cores are quieter but still have a nice rumble at idle and bark when the motor is rev'd. I'm very happy with them. I changed them out on the bike.
Removed the end caps.
Pulled out the cores and packing material.
Put in the new cores.
Repacked with the original packing material, using a long stick to push it in.
Replaced the end caps.
The hardest part was getting the end caps off. They were a tight fit, so they didn't just pull out.