Legal Question in Real Estate Law in California

I think your better approach to this problem is to confront (in a polite way, of course) the landlord and explain that a tenant is entitled to reasonable prior notice, unless there is an emergency. I think it is probably legally permissible for a tenant to re-key a lock, but don't even drill one additional hole, or you could be accused of making unauthorized modifications to the property. Even if you re-key, you won't solve the problem (if it is the landlord), because you'll have to give him/her new key right away to preserve his/her right of emergency access.