25 C.F.R. § 166.225
May a permittee voluntarily assign a leasehold interest under an approved encumbrance?
With our approval, under an approved encumbrance, a permittee voluntarily may assign the leasehold interest to someone other than the holder of a leasehold mortgage if the assignee agrees in writing to be bound by the terms of the permit. A permit may provide the Indian landowners with a right of first refusal on the conveyance of the leasehold interest.