(a) Subject to the power of a court of competent jurisdiction to remedy a defective execution of an imperative power of appointment, the directions of the donor as to the manner, time and conditions of the exercise of a power must be observed, except that:
(1) Where the donor has authorized it to be exercised by an instrument legally insufficient to dispose of the appointive property, the manner of exercise is to be determined by the provisions of this article.
(2) Where the donor has directed any formality to be observed in its exercise, in addition to those which would be legally sufficient to dispose of the appointive property, such additional formality is not necessary to a valid exercise of such power.
(3) Where the donor has made the power exercisable only by deed, it is also exercisable by a written will unless exercise by will is expressly excluded.
(4) Where the donor of a general power of appointment has not expressly imposed a requirement of good faith or of reasonableness with respect to the donee's exercise of such power, neither such requirement shall be implied.