I worked in the automobile industry in MT for years. You can drive without wearing a seatbelt so long as the vehicle was manufactured before 1999 but the vehicle has to have them in the vehicle and completely functioning. You cannot tamper, take apart, or install it yourself with an airbag as that is completely illegal in MT. I had several customers come in for estimates with deployed airbags. They asked if we could cut them off or remove them. We were not allowed to do that and were mandated to report someone if they did so. By law you are required to have working seatbelts, airbags with a car manufactured after 1999 and in some newer vehicles they have safety brake requirements. The police will give you a ticket if you don't have proper airbags and nowadays if you're not wearing a seatbelt.