You are of course always free to change your mind about your gift. You can amend your Will, by adding a codicil, at any time.  Do not write on or amend your existing Will as this could invalidate it. The Codicil has to be signed and witnessed in the same way as the Will itself, although the witnesses do not have to be the same. The Codicil must be kept with, but not affixed to, your Will.