The fascist +15% bonus effectiveness properly only applies while the country is fascist. That means that your permanent bonus percentages will change if you change governments to or from fascist. For example, suppose a fascist country has -96% building costs. The building costs bonus will drop to -83.2% if it changes governments to Monarchy. It will increase to -96% again if it changes back to fascist.

Does this also work the other way if you weren't Fascist before.

ie if you got to 83.2% as monarchy then switched FFO you would be at 96%?

That's how it's always worked.

Yes.

Thanks for the clarification!