If you decide to separate from your partner, it may be a good time to review your will to account for the change of circumstances or to reflect your new wishes. Unless you're making a very minor change (in a codicil) it's generally best to make a brand new Last will and testament which overrides your old will. You'll have to go through the same process of appointing executors and guardians (if necessary) and have it formally signed in the presence of two witnesses over 18.