MUTATION OF LIBEL, practice. An amendment allowed to a libel, by which there is an alteration of the substance of the libel, as by propounding a new cause of action, or asking one thing instead of another. Dunl. Adm. Pr. 213; Law's Eccl. Law, 165-167; 1 Paine's R. 435; 1 Gall. R. 123; 1 Wheat. R. 26l.