Super easy. Barely an inconvenience. I’ve done replacements on earpads myself a few times, on some ATH M50x and older Bose wired sets. One of my requirements for any headphone I buy is the ability to replace the pads for when I inevitably wear them out since they will probably go before the electronics do. I would give you some links to videos of how to or pages to buy replacements, but here’s the search I did. It’s all a gold mine for your purposes. https://www.google.com/search?q=qc35+ear+pads&rlz=1CAASUL_enUS871&oq=qc35+ear&aqs=chrome.0.0j69i57j0l4.3018j1j7&sourceid=chrome&ie=UTF-8