You can add a codicil yourself...quite easy...I know, I did myself and it's free.
ryck and I and pretty darn near everybody else are all in the same position, i.e., needing to leave at least one password behind, be it an Admin password (to unlock a keychain), or one to an app or to an encrypted sparse image such as I use to store my critical passwords, and that one password MUST be in the clear
somewhere.
Since
the added information would in no way change your will, though, should you decide to go that route, there's no need to either rewrite it or add a codicil. (I
emphatically note that depending upon your purpose, a codicil can be quite a lousy idea!!!) Simply staple a piece of paper to the original will, and the job is done.
What remains, of course, is to securely store that piece of paper.
Oops! Back to square one.