Updating an existing Will There may be changes in circumstances (births, deaths and marriages) as well as a change of heart that can affect your Will. The majority of minor changes can be covered by adding a codicil (an addition or alteration to a Will). A legacy gift to a charity can be added to an existing Will by codicil. The codicil must be signed and witnessed by two witnesses simultaneously and should be kept with the Will. Just speak to your solicitor.