If you are landlocked, and you are running steam, you would need some sort of qualification to do so. In New Jersey, you would need to be tested for a state Black Seal License (Boiler Operator - In Charge, what used to be called Fireman - In Charge) to be able to just steam it up (without using the steam, such as moving the loco). To be able to move it, you'd need a minimum Blue Seal Locomotive Engineer License. Boiler horsepower is another factor, if you own a big steam loco, you may need to upgrade to a Red Seal Engineer license.
Other states may require your insurance company to qualify you.
If you connect to outside lines, or cross public roadways and/or navigable waterways, you need federal qualifications and licensing.
If you run a landlocked diesel/gas unit, you probably won't need anything but the knowledge to run it.
With a couple of boiler failures over the last decade or so, live steamers and steam tractors have come under the scrutiny of the feds, calling them "antique and hobby boilers".
They tell me to act my age. I don't know how to do that. I've never been this old before.