Could freight steam engines heat passenger cars?

When passenger cars were heated by steam from the engine, could a freight engine pressed into service to rescue a passenger train provide such steam? I'd think there would have to be some kind of pressure-reducing valve to provide low-pressure steam, plus a suitable steam hose. But did all engines have some kind of pressure reducer to provide steam for the generator, air compressor, etc?
I guess the question really is, if a freight engine was needed for passenger service, what (if any) modifications would have to be done to enable it to provide steam heat, and could the modifications be done quickly in the roundhouse, etc, or would they require a shopping?

Hi Joe,
You are correct to assume the need for a pressure reducing device in order to heat the passenger cars. It consisted of a valve connected to the steam turret( main header) and piped under the locomotive's cab and tender to a flexible pipe(not a hose) that would connect to the passenger cars. This pipe was usually insulated with asbestos. Some freight engines were equipped with steam heat provisions. To equip a freight engine not so equipped would take at least a day, or more, if you had all the parts on hand. Not a quick job, but could probably be handled by the roundhouse crew.
As to the air pump and generator, they are equipped with governors to prevent them from running out of control, so they do take high pressure steam directly from the turret.
LF