A codicil is a document that allows you to amend your will without making a whole new will. It is usually used to make minor changes or to update one section.
I codicil still requires 2 independent witnesses to witness the testator’s signature. A witness cannot be a beneficiary or spouse of a beneficiary and you need an affidavit of subscribing witness for the Codicil. So for probate you have to have the affidavit for the execution of the will as well as the affidavit for the execution of the codicil.
Usually, you copy the section you are deleting and then write out the new section you are inserting.
Adding a codicil to a will is less costly than making a whole new will.