Rekey a lever lock
There are 3 ways to rekey a lever lock:
- file levers
- swap lever positions
- replace levers
- and arguably a fourth, modding the lock
Swap lever positions
The easiest option for 5 & 7 lever locks is to swap lever positions. The new lever arrangement must be symmetrical so the same key can operate it from both sides. So if the levers are numbered 1-5 from one side, 1&2 can be swapped, and 4&5 swapped.
This can't be done with 3 lever locks, or 2 lever locks that open from both sides. 2 lever locks that can only be opened from one side can have the levers swapped to make a new configuration.
Filing levers makes them rest in the correct unlocking position when the matching landing area on the key is deeper.
Its important that the newly filed surface is the correct shape. Where the surface is flat, scribe the lever before filing it. Where the surface is round, if you're determined enough to do it, scribe a rounded line a fixed distance from the old edge of the lever before filing.
Metal can be ground down by filing, milling or with a die grinder.
New sets of levers with matching keys can be bought & fitted to good quality locks. Its quick & easy, and often much cheaper than a new lock.
Having both new & old levers opens up lots of permutations to use in future.
Denting the side of the lock inward where the key turns is a basic way to stop unmodified keys operating the lock. Naturally this is only practical with thin walled locks, typically 2&3 lever types, and its possible to ruin a lock by doing it wrong. There's no need to symmetrically dent both sides, keys can be ground both sides to pass by a single dent.
The most controlled way to make a dent is to drill a hole in thick steel or a lump of wood, and place the lock casing over it. A hammer & nail does the job. Dishing the metal too far can jam the lock, or require so much metal removed from the key that it no longer works.
The purpose of this is simply to render any keys someone might have inoperable. It thus has the same effect as rekeying.
In principle lock modification voids any BS approval, which can affect house insurance if the policy requires a BS lock. In practice, denting a BS lock would be a challenge due to the thickness of metal, its the lighter 2 & 3 lever locks this is useful for.