Mont. Code § 25-4-601
When the answer of the defendant, expressly or by not denying, admits a part of the plaintiff's claim to be just, the court, upon the plaintiff's motion, may, in its discretion, order that the action be severed, that a judgment be entered for the plaintiff for the part admitted, and, if the plaintiff elects, that the action be continued with like effect with regard to the subsequent proceedings as if it had been originally brought for the remainder of the claim. The order must prescribe the time and manner of the plaintiff's election. If the plaintiff elects to continue the action, the plaintiff's right to costs upon the judgment is the same as if it were taken in an action brought for only that part of the claim. If the plaintiff does not elect to continue the action, costs must be awarded as upon final judgment in any other case.
§ 25-4-601, MCA