You can repack it, but if you do, don't pack it tightly around the core as this will give you a louder bike, with more power.. Instead, wrap it loosely and it should quiet down. Unfortunately doing this will not give you as much power ( it's not the end of the world :D )
Im not sure how much this will work on an aftermarket silencer, but at the very minimum it will take some 'bark' out..
** Silencer repacking is fairly easy, and not time consuming.. It should only take 10 minutes after you figure out how to seperate the core from the body... On my stock silencer I had to drill out the 3 rivets to pull it apart, and then use sheetmetal screws to put it back together.. **
( TIP: Use silicone around the end cap so when you put it back together it will seal nicely.. It might be a bit different with a 304 silencer, so if this TIP doesn't make sense, then don't worry about it!)
Good Luck!
Dan