A codicil is a testamentary instrument that alters, amends, or modifies specific provisions in a person’s previously executed will. The codicil does not revoke the will. It merely changes some of the provisions of the will. If you have a codicil, then both the will and the codicil are admitted to probate.
A codicil is best suited for making minor changes in the will. If on the other hand you are making major changes to the will, or if you have already written multiple codicils to your will, then you may be better off replacing your will with an entirely new will.
A codicil must be executed with the same formalities as a will. In other words, the codicil must be signed by the testator in the presence of witnesses.