Can an executor be added to a Will without having to redo the entire Will

He should redo his will to be safe. Adding extra clause and addendums will raise questions about there authenticity. In my opinion he should get a good trusts and estates lawyer to help him do it right so his wishes are respected.

There is no specific form for a will or a codicil (addendum to a will). Instead there are a few required components of a will such as witnesses, in writing, age, competency, etc. A codicil needs to meet the same requirements as a will with the added component that it properly references the will it is amending. Many estate planning attorneys find it just as easy to create a new document that does exactly what the client wants rather than amend a document that doesn't totally work.