Last year, when my daughter moved into her house, I put +Kwikset SmartKey door locks on for her. This week she decided she wanted to re-key and the whole job took less than a minute and only cost $10 each. With these locks, you put in the old key, turn 90 degrees, insert the special tool, pull out the old key, insert the new key and turn back. That's it, the lock is reprogrammed to the new key. The kit comes with 4 main keys plus 2 alternates. 

If you have someone coming in to do some work, you can quickly reprogram the lock to the alternate key, give it to someone one and when the job is done, you switch back to the original key.?