Welcome to the site !!
I am thinking about the mod you mentioned with the straight pipe , and just guessing here , but , I would think a straight pipe in there , instead of one with the holes , would just bypass and render the packing useless , as the holes are diffusers and what allows the exhaust to "flow" thru the packing , which in turn quiets the exhaust noise dramatically , so I am a bit confused as to why you would want to eliminate the inside baffle/diffuser , unless you have neighbors you just can't stand and want to annoy them with what would basically be a straight pipe
Unless you can explain what benefit swapping out the baffle with a straight tube actually accomplishes , i would say leave it be , because the packing won't be of any value with a straight pipe inside
As for replacing the packing , it should be like all the prior models beforehand , and you just drill out the rivets surrounding the endcap , and pull it off , and replace your packing and replace the endcap and instal new rivets