Mont. Code § 33-26-107
It is lawful for any executor, administrator, guardian, receiver, trustee, or other party of whom a bond, undertaking, or other obligation is required to agree with the entity's surety or sureties for the deposit of any or all money and assets for which the entity and the surety or sureties are or may be held responsible with a bank, savings bank, safe-deposit, or trust company, authorized by law to do business, or with another depository approved by the court or a judge, if the deposit is otherwise proper, for safekeeping, and in a manner that prevents the withdrawal of the money or assets or any part of the money or assets without the written consent of the surety or sureties or an order of court or a judge made on notice to the surety or sureties that the court or judge may direct. The agreement may not in any manner release from or change the liability of the principal or sureties as established by the terms of the bond.
§ 33-26-107, MCA