Mont. Code Ann. § 72-7-403
Method of release
72-7-403 . Method of release. A powerholder of a releasable power of appointment may release the power in whole or in part:
(1) by substantial compliance with a method provided in the terms of the instrument creating the power; or
(2) if the terms of the instrument creating the power do not provide a method or the method provided in the terms of the instrument is not expressly made exclusive, by a writing manifesting the powerholder's intent by clear and convincing evidence.