Had a friend who put an Akrapovic on his MT-07 - DB killer is welded but once you drill through a small part on the weld you can remove it/put it back easily and the drill hole is covered by carbon shield so unless they disassemble the shield to check (and my friend had it like this for 5 years before selling IIRC) it was just pull out - put it back in for technical
Generally, well designed bikes assume a certain pressure in the exhaust pipe and use it as a way to compute the internal combustion cycle timings, since it affects the movement of air and how long it stays and how fast it is likely to move on. So changing the pipes without doing anything indeed affects performance. That’s why most pipe changes usually also come with a reflash of the bike’s ECU so that the onboard computer can know new pipe’s air resistance parameters.