Normal rekeying is pretty easy, if you’re careful - push out the core (the “follower” will hold your spring pins in place), dump out the old key pins, swap to the new key, and put in the new key pins, replace the core. Even when I’ve completely screwed it up (pushed the follower too far so the springs came out, mixed all the key pins together so I had to work out which was which, and more) it’s not been more than a 10-minute job.