entry door lock replacement
If this is something you will only need to do one time, swap out the latchset. The chance of dropping the pins are high the first time around, but with care, it can be done. I know this from experience. The new latchset gives new longevity as well.

If this will be a recurring thing get the keying kit, I see them online and you can pick them up for as little as the cost of a new latchset, for the smaller kits. There are really cheap ones too, but I know nothing of what they have the capability of doing other than rekeying one knob.

I have no faith in the smartkey setup, but I am a purist when it comes to locks. I do not claim to know about smartkeys, but if it is a matter of putting in one key, installing a specific tool, and then put in the new key and remove the tool and it changes the lock, sounds like somebody with the original and a new key, and the same special tool can do the same.