A codicil is a new document you draft to amend your will. The codicil can change, add or remove any provision in the original will. The alternative to a codicil is to redraft the entire will, so a codicil will save you a lot of time.
Draft a republishing clause. For example, "I republish and reaffirm my last will and testament except for the following."
Write the substitution clause. For example, "I would like to substitute the following for Item I, Section A," followed by what you would like to substitute.
Follow the same attestation and affidavit requirements for a will in your state, including your signature on the codicil with the signatures of at least two witnesses.