An indenture may include a clause prescribing procedure by which the terms and conditions of the indenture may be subsequently amended or modified with the consent of the regents and the vote or written assent of the holders of a specified principal amount or specified proportion of the bonds issued and outstanding. Such clause may provide for meetings of bondholders and for the manner in which the consent of the bondholders may be given. The clause shall specifically state the effect of such amendment or modification upon the rights of the holders of all of the bonds and interest coupons appertaining to the bonds, whether attached to the bonds or detached from the bonds.