Stock mufflers will not really be packable. The reason is that there is almost no packing when new as they are more of a turbo style muffler than a "glass pack" design. Most aftermarket exhaust cans will be "glass pack designs and need repacking from time to time.
That said if you are asking if you can "core" them to convert them to a glass pack design the answer is maybe.
The monster cans were not the easiest to disassemble and due to the mounting method you need to keep some internals to have something to attach them with. the shop I used to work at cored plenty of exhausts by removing the internals and installing a perforated core that you then wrapped with packing material. we would not do Monsters as the labor costs involved made it more money that it was worth, your labor costs should be less
You will likely spend $20-40 for packing
$10-20 for core material
$20-30 for blind sealing rivets
if you can weld then you are good if not plan on another $50-60 at a welder
$10-20 for misc other bits and the rest is your labor
so if you do the labor converting should be in the $110-170 ish price range.
find a good set of used slip ons for not much more and spend more time riding.
Keep in mind you will likely need to add some fuel after making the exhaust less restrictive.