Mont. Code Ann. § 72-7-404
Revocation or amendment of release
72-7-404 . Revocation or amendment of release. A powerholder may revoke or amend a release of a power of appointment only to the extent that:
(1) the instrument of release is revocable by the powerholder; or
(2) the powerholder reserves a power of revocation or amendment in the instrument of release.