Mont. Code Ann. § 3-9-113

The judge may, upon the petition of a claimant or an insurer that the disability of the claimant has changed or that the claimant received benefits through fraud or deception, review, diminish, or increase, in accordance with the law on benefits as set forth in Title 39, chapter 71, any benefits previously awarded by the judge. An insurer's petition alleging that the claimant received benefits through fraud or deception must be filed within 2 years after the insurer discovers the fraud or deception.