If a power to appoint is or may be exercisable by two or more persons either in an individual or fiduciary capacity in conjunction with one another or successively, a release or disclaimer of the power in whole or in part executed by any one of the donees of the power shall be effective to release or disclaim, to the extent therein provided, all right of such person to exercise or to participate in the exercise of the said power, but unless the instrument creating the power otherwise provides, shall not prevent or limit the exercise or participation in the exercise thereof by the other donee or donees.