In the event that the endowments trust or the Fraser trustees wish to vary or revoke all or any of the terms of the Russell and Foster Endowment or the Fraser trust disposition, as the case may be, or enlarge the powers of the trustees of managing or administering any of the property subject to the said trusts, the endowments trust or the Fraser trustees, as the case may be, may apply to the Court of Session by Petition for an Order of the Court for such variation, revocation or enlargement.