The only set of rules that should concern you is the design code that governs your installation.
Both ASME B31.1 and B31.3 put limitations on use of cast iron in toxic, flammable and steam service. Limitations imposed typically are in the form of pressure/temperature maxima or inclusion only in non-shock service.
If a material is deemed suitable for service (by the piping code) and the component is design rated for that combination of temperature and pressure, then you should be able to use it. Automatic Control Valve manufacturers have excellent experience with succesful and non-successful installations and are usually happy to share it with a customer.
Gray cast iron, regard;ess of what you coat your wetted surfaces with, won't meet NACE MR0175 if that is a consideration.

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