A written revision to a Will is called a Codicil. An individual can have a Codicil to his or her Will as long as the Codicil meets certain requirements. The codicil must be signed and witnessed just as the original Will was signed and witnessed. The Codicil should refer to original Will by date and should be attached to the original Will. It is not recommended that an individual attempt to draft a codicil. A Codicil should only be drafted by an attorney to insure that it will have its intended effect.
Decades ago when Wills and documents were drafted on typewriters. Now with modern computers, it is usually better just to prepare a new Will drawn up and executed.
http://www.njlaws.com/codicil_to_a_will.html?id=107&a=
