Yes, we have extended gas mains into areas that were served by propane. Most ranges are easy to convert. They have adjustable orifices and regulators to change from propane to natural. Sometimes water heaters can be changed easily. Sometimes it requires completely changing out the burner and gas valve. Furnaces are the same. It can get expensive. The feds require equipment to be as efficient as possible now, and that means being designed for one fuel. Years ago, most equipment could be changed, by adjusting a regulator or they had adjustable orifices. Efficiency has greatly improved, but changing from one fuel to another is expensive. That is also the reason we try to maintain 1,000 Btu gas. If we have to mix, it is mixed to make 1,000 Btu's.