A beneficiary may disclaim any interest in whole or in part, or with reference to specific parts, shares, portions or assets thereof, by filing a disclaimer in the manner hereinafter provided. A guardian, executor, administrator or other personal representative of the estate of a minor, incompetent or deceased beneficiary, if he deems it in the best interests of those interested in the estate of such beneficiary and of those who take the beneficiary's interest by virtue of the disclaimer and not detrimental to the best interests of the beneficiary, with or without an order of the probate court, may execute and file a disclaimer on behalf of the beneficiary within the time and in the manner in which the beneficiary himself could disclaim if he were living, of legal age and competent. A beneficiary likewise may execute and file a disclaimer by agent or attorney so empowered.