Nothing in this chapter shall limit the power of a person who creates a trust after July 1, 1971, or the power of a person who has retained or has been granted the right to amend a trust created before July 1, 1971, to include a specific provision in the trust instrument or an amendment to the trust instrument as the case may be, which provides that some or all of the provisions of sections 634.2 and 634.3 shall have no application to such trust.
Iowa Code § 634.6