Mont. Code § 7-3-1211
The commission first elected may, at its first meeting, make an order that all existing ordinances and resolutions of some one city or town within the consolidated municipality which are of general application in such city or town shall be continued in force and be extended throughout the consolidated municipality, and a copy of such order must be published at least once in each newspaper printed and published within the consolidated municipality within 10 days after the making of such order. All other ordinances and resolutions of such city or town and all ordinances of all other cities and towns within the consolidated municipality, save and except ordinances and resolutions relating to public improvements to be paid for in whole or in part by special assessments, shall, upon the making of such order, be deemed repealed.
§ 7-3-1211, MCA